# Colors

Color (North American English) or colour (Commonwealth English) is the visual perceptual property corresponding in humans to the categories called red, blue, yellow, etc. Color derives from the spectrum of light (distribution of light power versus wavelength) interacting in the eye with the spectral sensitivities of the light receptors. Color categories and physical specifications of color are also associated with objects or materials based on their physical properties such as light absorption, reflection, or emission spectra. By defining a color space colors can be identified numerically by their coordinates.

## Quotes

* [P]ure light, such as that from the sun has no color, but is made colored by its degradation when interacting with objects having specific properties which then produce color.
** Aristotle (c. 350 BC) as quoted by Kurt Nassau, The Physics and Chemistry of Color: The Fifteen Causes of Color (1983) p. 4.
* [L]ight ...is the colour of the transparent medium contingently determined; for when anything of the nature of fire is found in the transparent medium its presence constitutes light, its absence darkness. ...[T]he transparent element is nothing which is found exclusively ...in any one of the substances ...it ...finds its existence in these bodies and subsists in varying degrees in the rest of material substances. ...[T]he Pythagorean terminology identified the visible superficies with colour. ...[C]olour exists in the boundary, but it by no means is the boundary of the body ...internally there exists the same constitution as externally displays colour. ...Colour ...is the limit of the transparent element in a determinately bounded body ...both in transparent substances ...and in those which appear to have a surface colour of their own. ...[T]hat, which in air causes light, may be present in the transparent medium or it may not ...[W]hite and black may be juxtaposed in such a way that by the minuteness of the division of its parts each is invisible while their product is visible, and thus colour may be produced. This product can appear neither white nor black ...it must be a sort of compound and a fresh kind of tint. ...[C]olours ...may be produced, and ...their multiplicity is due to differences in the proportion of their composition. ...[C]olours may ...be analogous to harmonies. ...[T]hose compounded according to the simplest proportions ...as is the case in harmonies, will appear to be the most pleasant ...e.g. purple, crimson ...This is one of the ways in which colours may be produced; a second is effected by the shining of one colour through another. This we may illustrate by the practice ...by painters when they give a wash of colour over another more vivid tint, when, for example, they wish to make a thing look as though it were in the water or in the air. ...[W]e may illustrate by the sun, which in itself appears white, but looks red when seen through mist and smoke. ...[W]e should have to suppose there was some ratio between the superficial and the underlying tints in ...some colours, while in others there would be ...lack of commensurate proportion. ...[Thus ...it is absurd to maintain, with the early philosophers, that colours are effluxes and that vision is effected by a cause of the efflux type. It was in every way binding on them to account for sensation by means of contact, and therefore it was obviously better to say that sensation was due to a movement set up by the sense object in the medium of sensation, and thus account for it by contact without the instrumentality of effluxes.] According to the theory of juxtaposition, just as we must assume that there are invisible spatial quanta, so must we postulate an imperceptible time to account for the imperceptibility of the diverse stimuli transmitted to the sense organ... But on the other theory there is no such necessity; the surface colour causes different motions in the medium when acted on and when not acted on by an underlying tint. Thus it appears to be something different, and neither black nor white. ...But let us premise that substances are mixed not merely in the way some people think by a juxtaposition of their ultimate minute parts ...imperceptible to sense but that they entirely interpenetrate each other in every part throughout ...The former theory accounts for the mixture only of those things which can be resolved into ultimate least parts ...On the other hand, things which cannot be resolved into least parts, cannot be mingled in this way; they must entirely interpenetrate each other; and these are the things which most naturally mix. ...[W]hen substances are mixed their colours too must be commingled, and that this is the supreme reason why there is a plurality of colours; neither superposition nor juxtaposition is the cause. In such mixtures the colour does not appear single when you are at a distance and diverse when you come near; it is a single tint from all points of view. The reason for the multiplicity of colours will be the fact that things which mix can be mixed in many different proportions ...[T]he same account will apply to the juxtaposition or superposition of colours as to their mixture. [T]hey, and likewise tastes and sounds, have definite species limited in number...
** Aristotle, De Sensu and De Memoria, III (c. 350 BC) Tr. G. R. T. Ross (1906) pp. 55-63.
* Colour has a logic as exact as that of form. One must not give up before capturing that first impression.
** Pierre Bonnard, Konstrevy (1937) as quoted in Pierre Bonard Observing Nature (2003) ed. Jorg Zutter, p. 27.
* There, for the price of just two sous, I found crépons and rice papers in astonishing colours. I covered the walls of my room with these naïve and gaudy pictures. ...It was not until much later that I became aware of the beauty of the great Japanese masters, more subdued by far, yet less elucidating in terms of pure colour.
** Pierre Bonnard, in Le Bonnard que je propose (1951) by Thadée Natanson, as quoted in Pierre Bonard Observing Nature (2003) ed. Jorg Zutter, p. 123.
* [Color effects] are never absolute but are relative to the total situation...
** Albert R. Chandler, Beauty and Human Nature: Elements of Psychological Aesthetics (1934) as quoted by Deborah T. Sharpe, The Psychology of Color and Design (1974)
* The colors of my life Are bountiful and bold, The purple glow of indigo, The gleam of green and gold. The splendor of the sunrise, The dazzle of a flame, The glory of a rainbow, I'd put 'em all to shame.
** Cy Coleman, Barnum (1980)
* When Michael saw this host, he first grew pale, As angels can; next like Italian twilight, He turned all colours—as a peacock's tail, Or sunset streaming through a Gothic Skylight In some old abbey, or a trout not stale, Or distant lightning on the horizon by night Or a fresh rainbow, or a grand review Of thirty regiments in red, green, and blue.
** Lord Byron, The Vision of Judgement (1820) LXI, as quoted in The Poetical Works of lord Byron, Complete in One Volume (1890) p. 520.
* From the mingled strength of shade and light A new creation rises to my sight, Such heav'nly figures from his pencil flow, So warm with light his blended colors glow.
** Lord Byron, Monody on the death of the Rt. Hon. R. B. Sheridan, Stanza 3. In Hoyt's New Cyclopedia Of Practical Quotations (1922), p. 576-77.
* Once a pallid vestal doubted truth in blue; Listed red as ruin, Harried every hue;Barracaded vision, garbed herself in sighs; Ridiculed the birth marks Of the butterfliesDormant and disdainful, Never could she see Why the golden powder Decorates the bee;Why a summer pasture Lends itself to paint; Why love unappareled Still remains the saint.Finally she faltered; Saw at last forsooth, Every gaudy color Is a bit of truth.
** Nathalia Crane (age, 11 yrs) The Vestal, The Janitor's Boy and Other Poems (1924) p. 32.
* Just as when painters are elaborating temple-offerings, men whom wisdom hath well taught their art,—they, when they have taken pigments of many colours with their hands, mix them in due proportion, more of some and less of others, and from them produce shapes like unto all things, making trees and men and women, beasts and birds and fishes that dwell in the waters, yea, and gods, that live long lives, and are exalted in honour,—so let not the error prevail over thy mind, that there is any other source of all the perishable creatures that appear in countless numbers. Know this for sure, for thou hast heard the tale from a goddess.
** Empedocles (c. 350 B.C.) Fragment 23, as quoted by John Burnet, Early Greek Philosophy (1920) p. 243. Note by Burnet: The "goddess" is, of course, the Muse. Cf. Fragment 5.
* Every one of the Impressionists examines the exact shade that is before his eyes and then matches it with the color on his palette and applies it to his canvas. But who can say that this color is the true color of that one minute? Even the artist himself has forgotten. All that mass of exact colors is lifeless, frozen. He lies stupidly...
** Paul Gauguin, as quoted by Charles Louis Borgmeyer, The Master Impressionists (1913) pp. 269-270.
* ...I am always between two currents of thought, first the material difficulties, turning round and round to make a living; and second, study of color. I am always in hope of making a discovery there, to express the love of two lovers by a marriage of two complementary colors, their mingling and their opposition, the mysterious vibrations of kindred tones. To express the thought of a brow by the radiance of a light tone against a sombre background. To express hope by some star, the eagerness of a soul by a sunset radiance. Certainly there is nothing in that of stereoscopic realism, but is it not some thing that actually exists?
** Vincent van Gogh, Letter to Theo, September 1888; as quoted in Vincent van Gogh, edited by Alfred H. Barr; Museum of Modern Art, New York, 1935, (letter 531) p. 22
* [S]timuli above adaptation reflectance are tinged with the hue of the illuminant, stimuli below adaptation levels are tinged with the afterimage complementary to the hue of the illuminant, and stimuli at or near adaptation reflectance are either achromatic or weakly saturated color of uncertain hue.
** Harry Helson, "Adaption Level Theory" Psychology (1959) ed. Sigmund Koch as quoted by Deborah T. Sharpe, The Psychology of Color and Design (1974)
* when the sun falls and we are all one color
** Linda Hogan (writer) Dark. Sweet.: New & Selected Poems (2014)
* In nature, light creates the color; in the picture, color creates light. Every color shade emanates a very characteristic light — no substitute is possible.
** Hans Hofmann, as quoted in Readings in American art, 1900 -1975 (1975) by Barbara Rose, p. 117
** Variant: In nature, light creates the color. In the picture, color creates the light.
* Color is that aspect of the appearance of objects and lights which depends upon the spectral composition of the radiant energy reaching the retina of the eye and upon its temporal and spatial distribution thereon.
** Dean B. Judd, Introduction to Color, Symposium on Color—Its Specification and Use in the Evaluation of Materials (March 5, 1941) American Society for Testing Materials, Washington Spring Meeting. STB50-EB/Jul. 1941, p. 1.
* I have a dream that my four little children will one day live in a nation where they will not be judged by the color of their skin but by the content of their character.
** Martin Luther King Jr, I Have a Dream (1963)
* When you go out to paint try to forget what object you have before you—a tree, a house, a field or whatever. Merely think, here is a little streak of blue, here an oblong of pink, here a streak of yellow, and paint it just as it looks to you, the exact color and shape, until it emerges as your own naive impression of the scene before you. I would like to paint the way a bird sings.
** Claude Monet, as quoted in The Artist (1957) Vol. 53-57, p. 24.
* I'm chasing the merest sliver of color. It's my own fault, I want to grasp the intangible. It's terrible how the light runs out, taking color with it. Color, any color, lasts a second, sometimes three of four minutes at the most.
** Claude Monet (c. 1918) as quoted by René Gimpel, Diary of an Art Dealer (1966) p. 58.
* I mix them with my brains, sir.
** John Opie, when asked with what he mixed his colors. See Samuel Smiles, Self Help, Chapter V. In Hoyt's New Cyclopedia Of Practical Quotations (1922), p. 576-77.
* Loudness depends on the quantity of the sound. Of the harmony of sounds I will hereafter speak. Colors are a flame which emanates from all bodies having particles corresponding to the sense of sight. Some of the particles are less and some greater, and some are equal to the parts of the sight. The equal particles are transparent, the larger contract, and the lesser dilate the sight; white is produced by the dilatation, black by the contraction, of the particles of sight. There is also a swifter motion of another sort of fire which forces a way into the passages of the eyes, and elicits from them a union of fire and water which we call tears. The fires from without and within meet and are extinguished in the tear-drop, and all sorts of colors are generated in the mixture. This affection is termed by us dazzling, and is produced by a flash. There is yet another sort of fire which mingles with the moisture of the eye without flashing, and produces a color like blood—to this we give the name of red. Again, the bright element mingling with the red and white produces a color which we call auburn. The law of proportion, however, in which the several colors are formed, cannot be determined scientifically or even probably. Red, when mingled with black and white, gives a purple hue, which becomes umber when the colors are burnt and a greater portion of black is added. Flame-color is a mixture of auburn and dun; dun of white and black; pale yellow of white and auburn. White and light meeting, and falling upon a full black, become dark blue; dark blue mingling with white becomes a light blue; the union of flame-color and black makes leek-green. There is no difficulty in seeing how other colors are probably composed. But he who should attempt to test the truth of this in fact, would forget the difference of the human and divine nature. God only is able to compound and resolve substances; such experiments are impossible to man.
** Plato, Timaeus (c. 360 BC) as quoted in The Dialogues of Plato (1911) Tr. Benjamin Jowett, Vol. 2 of 4, pp. 475-476.
* The fellow mixes blood with his colors.
** Guido Reni of Peter Paul Rubens. In Hoyt's New Cyclopedia Of Practical Quotations (1922), p. 576-77.
* Transport these Mornings on the Seine, Wheatstacks, and Cathedrals around the world and no matter where these paintings will be, the spectator will admire and envy a country where the hand of man built such monuments in the middle of such beautiful sites. Glory thus to the artist, who with the aid of a few lines and some dashes of color can so grandly synthesize the land where he lives.
** Charles Saunier on works of Claude Monet, "Petit Gazette d'art: Claude Monet", La Revue blanche, Vol. 22, No. 181 (Dec 15, 1900) p. 624, as quoted by Paul Hayes Tucker, Claude Monet Life and Art (1995) pp.185-186.
* I've fought the good fight. And now it’s all over, there's an indescribable peace. ...I believe in Michelangelo, Velásquez and Rembrandt; in the might of design, the mystery of color, the redemption of all things by beauty everlasting and the message of Art that has made these hands blessed. Amen. Amen.
** George Bernard Shaw, The Doctor's Dilema (1906) Act IV, Spoken by the painter, Louis.
* In regard to the life of every one, whether man, spirit, or angel... it flows in from the Lord alone, who is life itself... But the life which flows in is received by every one according to his character; good and truth are received as good and truth by the good; while by the evil good and truth are received as evil and falsity, and are even changed into evil and falsity in them. It is comparatively as the light of the sun; which diffuses itself into all objects on the earth, but is received according to the quality of each object, and becomes of a beautiful colour in beautiful forms, and of an ugly colour in ugly forms. ...But I know the fallacy will prevail with many that they will of themselves, and think of themselves, and so of themselves have life, when yet nothing is less true.
** Emanuel Swedenborg, Free Will, A Compendium of the Theological Writings of Emanuel Swedenborg (1888) ed. Samuel M. Warren, p. 272.
* If you mean that the proximity of one color should give beauty to another that terminates near it, observe the rays of the sun in the composition of the rainbow, the colors of which are generated by the falling rain, when each drop in its descent takes every color of the bow.
** Leonardo da Vinci Treatise on Painting (c. 1490)
* I think it pisses God off if you walk by the color purple in a field somewhere and don’t notice it.
** Alice Walker, The Color Purple (1982)
* The terms relative to colour, occurring in the Bible, may be arranged in two classes, the first including those descriptive of natural objects, the second the artificial mixtures employed in dyeing and painting. ...[A]n exact terminology of colours is of modern growth. Ancient peoples, even so artistic a nation as the Greeks, used the names of colours very vaguely. The Hebrews had not the artistic faculty at all strongly developed, and their names for colours, especially those of the first class, cannot be interpreted in any hard and fast manner. (1) The natural colours noticed in the Bible are white, black, red, yellow and green. ...green is apparently applied more to the freshness and beauty of vegetation than to... colour; while yellow (used very seldom) is difficult to discriminate from some shade of green. White is prominent, especially as representing light, which deeply impressed the Heb. mind... by its divine symbolism, and its profound moral connotation. Black is prominent also as the physical and moral opposite of white... Red was also vividly appreciated by the Hebrew, as the colour of blood (the sacred principle of life), of wine, and of many natural objects, especially perhaps the red soil and red cliffs... (2) Artificial colours. ...there is no evidence ...that the Hebrews of the period of the Exodus were themselves acquainted with the art of dyeing. They were probably indebted ...to the Egyptians and the Phoenicians, to the latter for the dyes and to the former for the processes. The principal dyes were purples, light and dark... and crimson... Vermilion was introduced at a late period. (a) Purple... well known and valued over the whole ancient world, was obtained from the secretion of a... shell-fish, the Murex trunculus of Linnaeus... probably a lighter shade, in which red predominated over blue; while the darker purple, a violet was produced from another species of shell-fish. ...Robes of purple were the characteristic decoration in antiquity of kings... the highest officers, civil and religious ...the wealthy and luxurious ...(b) Blue This dye was procured from a species of shell-fish found on the coast of Phoenicia, and called by modern naturalists Helix lanthina. ...it was emblematic of ...the deep, dark hue of the Eastern sky. (c) Scarlet (crimson...) [T]he worm or grub whence the dye was procured... was a cochineal insect... found in considerable quantities in Armenia, Palestine, and other Eastern countries... ) The tint produced was crimson rather than scarlet. The only natural object to which it is applied in Scripture is the lips... It was the characteristic colour of the soldier's dress, especially in the Roman armies. (d) Vermilion... was a pigment of mineral extraction used in fresco paintings... or for decorating the walls and beams of houses... Vermilion was a favourite colour among the Assyrians... Symbolical and mystical meanings of colours. ...White is associated with moral purity and innocence ...with joy, festival, and victory ...Black is the symbol of evil, misery, and death ...Red and also scarlet are connected ...with war and bloodshed ...A deeper significance, more appropriate to the special divine purpose ...particularly in the three characteristic colours of the tabernacle hangings, the cloths of service, and the vestments of the high-priest. Blue, purple, and scarlet frequently occur; and as purple is produced by the mixing of the other two, it has been remarkably suggested by some writers that, as blue is the colour of the sky, and scarlet of human life or blood (note ...the etymological connexion between ādām, "man," and ādâm, "to be red"), so the combination of the two is intended to suggest the Incarnation. ...[I]n the theophanies of Ezk.8.2, Rev.4.3, two different tints are alluded to (a bright white and a glowing red), which have been thought to suggest the two aspects of God's moral nature, light and fire, mercy and justice; or love in its two aspects of pardon and correction. ...[T]he colours of the Bible convey in many cases more than the literal meaning...
** Reverand A. R. Whitham, Colours, The Illustrated Bible Dictionary (1908) ed. Rev. William C. Piercy, pp. 172-173.
* This pencil take (she said), whose colours clear Richly paint the vernal year:
** Thomas Gray, "The Progress of Poesy: A Pindaric Ode" (1757), III.1.
* The houses are haunted By white night-gowns. None are green, Or purple with green rings, Or green with yellow rings, Or yellow with blue rings. None of them are strange, With socks of lace And beaded ceintures. People are not going To dream of baboons and periwinkles. Only, here and there, an old sailor, Drunk and asleep in his boots, Catches tigers In red weather.
** Wallace Stevens, "Disillusionment of Ten O’Clock", Rogue (1915); Harmonium (1923)

### De Coloribus (c. 300 B.C.)

    On Colors (Greek Περὶ χρωμάτων) is attributed to Aristotle, but ascribed to Theophrastus or Strato of Lampsacus by some authorities. Tr. (1913) by T. Loveday & E. S. Forster in The Works of Aristotle (1913) ed. W. D. Ross, Vol VI.
* Simple colours are the proper colors of the elements, i.e., of fire, air, water, and earth. Air and water when pure are by nature white, fire (and the sun) yellow, and earth is naturally white. The variety of hues which earth assumes is due to coloration by tincture... Black is the proper colour of elements in process of transmutation. The remaining colours... arise from blending by mixture of these primary colours.
** 791$^a$, 1-13.
* There are many arguments to prove that darkness is not a colour, but merely privation of light...
** 791$^b$, 2-4.
* From these primary colours the rest are derived in all their variety of chromatic effects by blending of them and by their presence in varying strengths. ...[M]ixture of white with black ...gives grey. ...[A] dusky black mixed with light gives crimson. ...[A] vivid bright violet is obtained from a blend of feeble sunlight with a thin dusky white. That is why the air sometimes looks purple at sunrise and sunset... So, too, the sea takes a purple hue when the waves rise so that one side of them is in shadow...
** 792$^a$, 2-23.
* [W]e must not proceed in this inquiry by blending pigments as painters do, but rather by comparing the rays reflected from the aforesaid known colours, this being the best way of investigating the true nature of colour-blends.
** 792$^b$, 15.
* [V]ariations of tint occur: 1) Because colours are introcepted by varying and irregular strengths of light and shade. ...(2) because the colours blent vary in fullness and in effectiveness. ...(3) because they are blent in different proportions. ...(4) Difference of hue may also depend on the relative brightness and lustre or dimness and dullness of the blend. Lustre is simply continuity and density of light... (5) some objects change their colour and assume a variety of hues when polished by rubbing or other means, like silver, gold, copper, and iron, when they are polished...(6) In the case of objects burning, dissolving, or melting in the fire, we find that those have the greatest variety which are dark in colour... (7) Apart from these cases, variety of hue is characteristic of all dark smooth objects, such as water, clouds, and birds plumage. ...(8) Lastly, we never see a colour in absolute purity: it is always blent, if not with another colour, then with rays of light or with shadows, and so it assumes a new tint.
** 793$^a$-793$^b$
* [O]bjects assume different tints ...when seen by firelight or moonlight or torchlight, because the colours of those lights differ somewhat. They vary also in consequence of mixture with other colours, for when coloured light passes through a medium of another colour it takes a new tinge.
** 793$^b$, 17-24.
* [L]ight when it reaches the eye may be a blend of many colours, though the sensation produced is not of a blend but of some colour, predominant in the blend. This is why objects under water tend to have the colour of water, and why reflections in mirrors resemble the colour of the mirrors, and we must suppose that the same thing happens in the case of air.
** 793$^b$, 27-34.
* Thus all hues represent a threefold mixture of light, a translucent medium (e.g. water or air), and underlying colours from which the light is reflected.
** 794$^a$
* Coloration may also be due to a process of tincture or dyeing, when one thing takes its hue from another. Common sources of such coloration are the flowers of plants and their roots, bark, wood, leaves, or fruit, and again, earth, foam, and metallic inks. Sometimes coloration is due to animal juices (e.g. the juice of the purple-fish, with which clothes are dyed violet), in other cases to wine, or smoke, or lye mixture, or to sea-water... In short, anything that has a colour of its own may transfer that colour to other things, and ...colour leaving one object passes with moisture and heat into the pores of another... Furthermore, steeping material to be dyed in different astringent solutions during the dyeing produces a great variety of hues and mixtures, and these are also affected by the condition of the material itself...
** 794$^a$ 16-33.
* [I]n hair and feathers of every kind, changes always occur either... when the nutriment in them fails, or when, on the contrary, it is too abundant. Therefore the age at which the hair is at its whitest or blackest varies in different cases... But hair is never crimson or violet or green or any other colour of that kind, because all such colours arise only by mixture with the rays of the sun, and further because in all hairs which contain moisture the changes take place beneath the skin, and so they admit of no admixture. ...Thus in birds, as in plants, the maturation of the colours takes place outside the body. So, too, the other forms of animal life aquatic creatures, reptiles, and shell-fish have all sorts and manners of colouring, because in them too the process of maturation is violent. From what has been set forth in this treatise one may best understand the scientific theory of colours.
** 799$^a$-799$^b$.

### Leonardo Da Vinci's Note-Books (c. 1472-1519; Tr. 1906)

    : Arranged and rendered into English with Introductions (1906) by Edward McCurdy. Note: page number links below are to the 1923 edition.
* [T]hings seen through the mist are similar in colour to those which are at a distance...
** Book II. Nature, Explanation of Why the Sun Seems Larger in the West (A 64 v.) p. 87.
* [T]he blue which is seen in the atmosphere is not its own colour, but is caused by the heated moisture having evaporated into the most minute imperceptible particles, which the beams of the solar rays attract and cause to seem luminous against the deep intense darkness of the region of fire that forms a covering above them. ...As a further example of the colour of the atmosphere, we may take the case of the smoke produced by old dry wood, for as it comes out of the chimneys it seems to be a pronounced blue when seen between the eye and a dark space, but as it rises higher and comes between the eye and the luminous atmosphere, it turns immediately to an ashen grey hue, and this comes to pass because it no longer has darkness beyond it... But if this smoke comes from new green wood, then it will not assume a blue colour, because... it is not transparent... [I]f the atmosphere had this transparent blue as its natural colour, it would follow that wherever a greater quantity of atmosphere came between the eye and the fiery element, it would appear of a deeper shade of blue, as is seen with blue glass and with sapphires, which appear darker in proportion as they are thicker. ...We may also observe the difference between the atoms of dust and those of the smoke seen in the sun’s rays as they pass through the chinks of the walls in dark rooms, that the one seems the colour of ashes, and the other—the thin smoke—seems of a most beautiful blue. We may see also, in the dark shadows of mountains, far from the eye, that the atmosphere which is between the eye and these shadows will appear very blue, and in the portion of these mountains which is in light, it will not vary much from its first colour.
** Of the Colour of the Atmosphere (Leic. 4 a [R 300]) pp. 126-129.
* But whoever would see a final proof, should stain a board with various different colours, among which he should include a very strong black, and then over them all he should lay a thin, transparent white, and he will then perceive that the lustre of the white will nowhere display a more beautiful blue than over the black,—but it must be very thin and finely ground.
** Of the Colour of the Atmosphere (Leic. 4 a [R 300]) p. 129.
* So the atmosphere appears blue because of the darkness which is beyond it; and if you look towards the horizon of the sky, you will see that the atmosphere is not blue, and this is due to its density; and so at every stage as you raise your eye up from this horizon to the sky which is above you, you will find that the atmosphere will seem darker, and this is because a lesser quantity of air interposes between your eye and this darkness. And if you are on the top of a high mountain the atmosphere will seem darker above you just in proportion as it becomes rarer between you and the said darkness; and this will be intensified at every successive stage of its height, so that at the last it will remain dark.
** Of the Colour of the Atmosphere (F 18 r.) p. 129.
* The mind of the painter should be like a mirror which always takes the colour of the thing that it reflects and which is filled by as many images as there are things placed before it. ...And do not after the manner of some painters who when tired by imaginative work, lay aside their task... keeping... such weariness of mind as prevents them either seeing or being conscious of different objects; so that often when meeting friends or relatives, and being saluted by them, although they may see and hear them they know them no more than if they had met only so much air.
** Book III. Art, 2. The Precepts of the Painter: Painting (MS. 2038, Bib. Nat. 2 r.) pp. 163-164.
* When such is the condition of night, if you wish to re¬present a scene therein, you must arrange to introduce a great fire there, and then the things which are nearest to the fire will be more deeply tinged with its colour, for whatever is nearest to the object partakes most fully of its nature; and making the fire of a reddish colour you should represent all the things illuminated by it as being also of a ruddy hue, while those which are farther away from the fire should be dyed more deeply with the black colour of the night.
** Of the Way to Represent a Night Scene (MS. 2038, Bib. Nat. 18 v.) p. 193.
* There is another kind of perspective which I call aerial, because by the difference in the atmosphere one is able to distinguish the various distances... and if in painting you wish to make one seem further away than another you must make the atmosphere somewhat heavy. ...[I]n an atmosphere of uniform density the most distant things seen through it, such as the mountains, in consequence of the great quantity of atmosphere which is between your eye and them, will appear blue... Therefore you should make the building which is nearest... of its natural colour, and that which is more distant make less defined and bluer; and one which you wish should seem as far away again make of double the depth of blue, and one you desire should seem five times as far away make five times as blue.
** Of Aerial Perspective (MS. 2038, Bib. Nat. 25 v.) pp. 213-214.
* An object of uniform thickness and colour seen against a background of various colours will appear not to be of uniform thickness. And if an object of uniform thickness and of various colours is seen against a background of uniform colour the object will seem of a varying thickness. And in proportion as the colours of the background, or of the object seen against the background, have more variety, the more will their thickness seem to vary...
** Book III. Art, 3. Perspective and Light and Shade: Of Ordinary Perspective (I 17 v.) pp. 214-215.
* A dark object seen against a light background will seem smaller than it is. A light object will appear greater in size when it is seen against a background that is darker in colour.
** Of Ordinary Perspective (I 18 r.) p. 215.
* The first requisite of painting is that the bodies which it represents should appear in relief, and that the scenes which surround them with effects of distance should seem to enter into the plane in which the picture is produced by means of the three parts of perspective, namely the diminution in the distinctness of the form of bodies, the diminution in their size, and the diminution in their colour. Of these three divisions of perspective the first has its origin in the eye, the two others are derived from the atmosphere that is interposed between the eye and the objects which the eye beholds.
** Of the Requisites of Painting (E 79 v.) pp. 215-216.
* There are three divisions of perspective as employed in painting. Of these the first relates to the diminution in the volume of opaque bodies; the second treats of the diminution and disappearance of the outlines of these opaque bodies; the third is of their diminution and loss of colour when at a great distance.
** Of Painting and Perspective (E 80 v.) pp. 218.
* It seems to me that the shadows are of supreme importance in perspective, seeing that without them opaque and solid bodies will be indistinct... as to their boundaries..., unless these are seen against a background differing in colour... [E]very opaque body is surrounded and has its surface clothed with shadows and lights... [T]hese shadows are... of varying degrees of darkness... caused by the absence of a variable quantity of luminous rays; and these I call primary shadows... From these primary shadows there issue certain dark rays which... vary in intensity according to the varieties of the primary shadows... I call these shadows derived shadows... [D]erived shadows in striking upon anything create as many different effects as are the different places... And since where the derived shadow strikes, it is always surrounded by the striking of the luminous rays, it leaps back with these in a reflex stream towards its source and meets the primary shadow, and mingles with and becomes changed into it... In addition... many different varieties of the rebound of the reflected rays which will modify the primary shadow by as many different colours as there are different points from whence these luminous reflected rays proceed. ...[V]arious distances ...may exist between the point of striking of each reflected ray and the point from whence it proceeds, and [it acquires] various different shades of colour... in striking against opaque bodies.
** Shadow is the Withholding of Light (C. A. 250, r. a.) pp. 219-221.
* [Y]ou should not make the shadows end like stone, for the flesh retains a slight transparency, as may be observed by looking at a hand held between the eye and the sun, when it is seen to flush red and to be of a luminous transparency. And let the part which is brightest in colour be between the lights and the shadows.
** (MS. 2038, Bib. Nat. 31 v.) pp. 221-222.
* Shadows become lost in the far distance, because the vast expanse of luminous atmosphere which lies between the eye and the object... suffuses the shadows of the object with its own colour.
** Of Shadows in the Far Distance (MS. 2038, Bib. Nat. 20 v.) p. 224.
* When you are representing a white body surrounded by ample space, since the white has no colour in itself it is tinged and in part transformed by the colour of what is set over against it. If you are looking at a woman dressed in white in the midst of a landscape the side... exposed to the atmosphere... since this atmosphere is itself blue, the side of the woman which is exposed to it will appear steeped in blue. ...[A]ll the parts of the folds [of her dress] which are turned towards the meadow will be dyed by the reflected rays to the colour of the meadow; and thus she becomes changed into the colours of the objects near, both those luminous and those nonluminous.
** How White Bodies Ought to be Represented (MS. 2038, Bib. Nat. 20 r.) pp. 227-228.
* Of colours of equal whiteness that will seem most dazzling which is on the darkest background, and black will seem most intense when it is against a background of greater whiteness. Red also will seem most vivid when against a yellow background, and so in like manner with all the colours when set against those which present the sharpest contrast.
** Of Colours (C. A. 184 v. c.) p. 228.
* [W]hen a white object is seen in the open air... shadows are blue... in accordance with the fourth proposition—'the surface of every opaque body partakes of the colour of surrounding objects.' ...that part which is not exposed to the sun remains in shadow, and only partakes of the colour of the atmosphere. And if this white object should neither reflect the green of the fields which stretch out to the horizon nor... face the brightness of the horizon itself, it would undoubtedly appear of such simple colour as the atmosphere showed itself to be.
** Painting (F 75 r.) p. 229.
* The colour of the object illuminated partakes of the colour of that which illuminates it.
** Of Painting (G 37 r.) p. 229.
* Since... the quality of colours becomes known by means of light... where there is most light there the true quality of the colour so illuminated will be most visible, and where there is most shadow there the colour will be most affected by the colour of the shadow. Therefore, O painter, be mindful to show the true quality of the colours in the parts which are in light.
** Why Beautiful Colours Should be in the Lights (MS. 2038, Bib. Nat. 33 r.) p. 233.

### Opticks (1704)

    by Sir Isaac Newton
* Lights which differ in Colour, differ also in Degrees of Refrangibility.
** Proposition 1, Theorem 1, p. 13.
* [W]ith a Perpendicular right Line drawn cross from one Side to the other, distinguished it into two equal Parts. One of these Parts I painted with a red Colour and the other with a blew. The Paper was very black, and the Colours intense and thickly laid on... This Paper I viewed through a Prism of solid Glass... Beyond the Prism was the Wall of the Chamber under the Window covered over with black Cloth, and the Cloth was involved in Darkness... These things being thus ordered, I found... the Light which comes from the blew half of the Paper through the Prism to the Eye, does... suffer a greater Refraction than the Light which comes from the red half, and by consequence is more refrangible.
** Experiment 1, pp. 13-14.
* [T]his Light being trajected only through the Parallel Superficies of the two Prisms, if it suffered any change by the Refraction of one Superficies it lost that impression by the contrary Refraction of the other Superficies, and so being restored to its pristine constitution became of the same nature and condition as at first before its Incidence on those Prisms and therefore, before its Incidence, was as much compounded of Rays differently Refrangible as afterwards.
** Experiment 10, p. 40.
* [T]he Sun's Light is an Heterogeneous mixture of Rays, some of which are constantly more Refrangible then others...
** Scholium, p. 44.
* [I]n these three Experiments... the Colour of Homogeneal Light was never changed by the Refraction.
** Experiment 14, p. 53.
* Do not the Rays which differ in Refrangibility differ also in Flexibility; and are they not by their different inflexions separated from one another, so as after separation to make the Colours in the three Fringes... ? And after what manner are they inflected to make those Fringes?
** Query 2, p. 132.
* Are not the Rays of Light in passing by the edges and sides of Bodies, bent several times backwards and forwards, with a motion like that of an Eel? And do not the three Fringes of colour'd Light... arise from three such bendings?
** Query 3, p. 133.
* Do not several sorts of Rays make Vibrations of several bignesses, which according to their bigness excite Sensations of several Colours, much after the manner that the Vibrations of the Air, according to their several bignesses excite Sensations of several Sounds? And particularly do not the most refrangible Rays excite the shortest Vibrations for making a Sensation of deep violet, the least refrangible the largest form making a Sensation of deep red, and several intermediate sorts of Rays, Vibrations of several intermediate bignesses to make Sensations of several intermediate Colours?
** Query 13, p. 136.

### Goethe's Theory of Colours (1840)

    Tr. with notes by Charles Lock Eastlake, of Johann Wolfgang von Goethe, Zur Farbenlehre (1810)
* [T]he eye sees no form, inasmuch as light, shade, and colour together constitute that which to our vision distinguishes object from object, and the parts... From these three, light, shade, and colour, we construct the visible world, and thus... make painting possible, an art which has the power of producing on a flat surface a much more perfect visible world than the actual one can be.
** Introduction, pp. xxxviii-xxxix.
* [C]olour is a law of nature in relation with the sense of sight... an elementary phenomenon in nature adapted to the sense of vision; a phenomenon which, like all others, exhibits itself by separation and contrast, by commixture and union, by augmentation and neutralization, by communication and dissolution: under these general terms its nature may be best comprehended.
** Introduction, p. xl.
* From time immemorial it has been dangerous to treat of colour; so much so, that one of our predecessors ventured on a certain occasion to say, The ox becomes furious if a red cloth is shown to him; but the philosopher, who speaks of colour only in a general way, begins to rave.
** Introduction, pp. xl-xli.
* [W]e must begin by explaining how we have classed the different conditions under which colour is produced. We found three modes... three classes... or rather three exhibitions of them all. ...[W]e considered colours, as far as they... belong to the eye itself, and to depend on an action and re-action of the organ; next... as perceived in, or by means of, colourless mediums; and lastly... as belonging to particular substances. We have denominated the first, physiological, the second, physical, the third, chemical colours. The first are fleeting and not to be arrested; the next are passing, but... for a while enduring; the last may be made permanent for any length of time.
** Introduction, p. xli.
* [L]ight and darkness, brightness and obscurity, or... light and its absence, are necessary to the production of colour.
** Introduction, p. xlii.
* Next to the light, a colour appears which we call yellow; another appears next to the darkness, which we name blue. When these, in their purest state, are so mixed that they are exactly equal, they produce a third colour called green. ...[T]he intensest and purest red, especially in physical cases, is produced when the two extremes of the yellow-red and blue-red are united.
** Introduction, p. xlii.
* With these three or six colours, which may be conveniently included in a circle, the elementary doctrine of colours is alone concerned.
** Introduction, p. xliii.
* [C]olours throughout are to be considered as half-lights, as half-shadows, on which account if they are so mixed as reciprocally to destroy their specific hues, a shadowy tint, a grey, is produced.
** Introduction, p. xliii.
* [I]f the Newtonian doctrine was easily learnt, insurmountable difficulties presented themselvse in its application. Our theory is perhaps more difficult to comprehend, but once known, all is accomplished, for it carries its application along with it.
** Introduction, p. xlv.
* Everything living tends to colour—to local, specific colour, to effect, to opacity—pervading the minutest atoms. Everything in which life is extinct approximates to white... to the abstract, the general state, to clearness, to transparence.
** 586, p. 234.

### Letters of a Post-Impressionist (1912)

    :Being the Familiar Letters of Vincent van Gough Tr. Anthony M. Ludovici. [Note: quotes below are for the most part, from letters written during his period as an active painter, between 1882 and 1890, the year of van Gough's death.]
* I am at work upon a portrait of our mother; as I could no longer endure the sight of the black photograph. I do not wish to possess black photographs, and yet I certainly wish to have a portrait of our mother.
** Letter to Theo (August, 1887) p. xxxii.
* Dear Brother, ...Last Sunday I began something which I had had in mind for many a day: It is the view of a flat green meadow, dotted with haycocks. A cinder path running alongside of a ditch crosses it diagonally. And on the horizon, in the middle of the picture, there stands the sun. The whole thing is a blend of colour and tone a vibration of the whole scale of colours in the air. First of all there is a mauve tinted mist through which the sun peers, half concealed by a dark violet bank of clouds with a thin brilliant red lining. The sun contains some vermilion, and above it there is a strip of yellow which shades into green and, higher up, into a bluish tint that becomes the most delicate azure. Here and there I have put in a light purple or gray cloud gilded with the sun's livery. The ground is a strong carpet-like texture of green, gray and brown, full of light and shade and life. The water in the ditch sparkles on the clay soil. It is in the style of one of Emile Breton's paintings. I have also painted a large stretch of dunes. I put the colour on thick and treated it broadly. I feel quite certain that, on looking at these two pictures, no one will ever believe that they are the first studies I have ever painted. ...I believe the reason of it is that before I began to paint, I made such a long and careful study of drawing and perspective that I can now sketch a thing as I see it. ...[S]ince I have bought my brushes and painting materials, I have slaved so hard that I am dead tired—seven colour studies straight off! ...I literally cannot stand, and yet I can neither forsake my work nor take a rest. ...[W]hen I am painting things present themselves to me in colour, which formerly I never used to see things full of breadth and vigour. ...I have progressed to the extent that when anything in Nature happens to strike me, I have more means at my command ...for expressing that thing with force.
** Letter to Theo, pp. 3-5.
* Yesterday evening I was busy painting the gently rising ground in the wood, which is all strewn with dry withered beach leaves. It varied in colour from a light to a dark red-brown, and the cast shadows of the trees fell across it in faint or strongly marked stripes. The difficulty was and I found it very trying to succeed in getting the depth of the colour and the enormous strength and solidity of the ground and I noticed while I worked how much light there was even in the dark shadows! The thing was to render the effect of light and also the glow, and not to lose the depth of rich colour. For one cannot imagine a more magnificent carpet than that deep red-brown ground, bathed in the glow of the autumn evening sunlight, softened by its passage through the trees. Beech trees grow here, the trunks of which look bright green in the clear light and a warm black-green in the shade. Behind the trunks, above the red-brown ground one could see the delicate blue and warm gray of the sky—it was scarcely blue—and in front of it a diaphanous haze of green, and a maze of trees with golden leaves. The forms of a few peasants gathering wood crept about like dark mysterious shadows, while the white bonnet of a woman bending to gather a few dried twigs suddenly stood out from the deep red-brown of the earth. ...The white bonnet, the shoulders, and bust of a woman stood out against the sky. The figures were large and full of poetry and, in the twilight of the deep shadows, seemed like gigantic terracottas fashioned in a studio. That is how I describe Nature to you. How far I have rendered the effect in my sketch, I do not know. I can only say that I was struck by the harmony of green, red, black, yellow, blue, and gray. It was quite in the style of de Groux; the effect was like that in the sketch of the "Depart du Consent." To paint it was a herculean task. On the ground alone I used one and a half large tubes of white; and yet it is still very dark. I also used red, yellow, brown, yellow-ochre, black, raw sienna and bistre and the result is a red-brown, which varies from a deep wine-red to a delicate pale pink. It is very difficult to succeed in getting the colour of the moss and the effect of the small border of fresh grass which shone so brightly in the sunlight. Believe me, this is a sketch which, if I may say so, people will think something of, for it makes a decided appeal. ...I pressed the roots and trunks out of the tubes direct, and then modelled them a little with the brush. And now they do indeed stand in the soil, and grow out of it, and strike firm roots into it. ...In a sense I am glad that I never learnt to paint. If I had I should perhaps have learnt to overlook such effects.
** Letter to Theo, pp. 12-15.
* The great doctrine bequeathed to us by the Dutch masters is, I think, as follows: Line and colour should be seen as one, a standpoint which Bracquemond also holds. But very few observe this principle, they draw with everything, save with good colour.
** Letter to Theo, p. 27.
* [W]hile contemplating Hals, Rembrandt, Ruysdael, and others, I constantly thought of the saying, that when Delacroix paints, it is exactly like a lion devouring a piece of flesh. How true that is! And, Theo, when I think of what one might call "the technique crew" how tedious they all are! ...For is it not exasperating to see the same dodges everywhere... everywhere the same tedious gray-white light, in the place of light and chiaroscuro, colour, local colour instead of shades of colour... Colour as colour means something ...That which has a ...really beautiful effect, is also right. When Veronese painted the portraits of his beau monde in the "Marriage at Cana," he used all the wealth of his palette in deep violets and gorgeous golden tones for the purpose, while he also introduced a faint azure blue and a pearly white which do not spring into the foreground. He throws it back, and it looks well in the neighbourhood of the sky and of the marble palaces, which strangely complete the figures; it changes quite of its own accord. The background is so beautiful that it seems to have come into being quite naturally and spontaneously out of the colour scheme. ...The point is to think about a thing, to consider its surroundings, and to let it grow out of the latter. ...I do not wish to argue studying from Nature or the struggling with reality, out of existence; for years I myself worked in this way with almost fruitless and, in any case, wretched results. ...One begins by plaguing one's self to no purpose in order to be true to nature ...But these two methods cannot be pursued together. Diligent study, even if it seem to be fruitless, leads to familiarity with nature and to a thorough knowledge of things. The greatest and most powerful imagination has also been able to produce things from reality, before which people have stood in dumb amazement.
** Letter to Theo, pp. 29-31.
* I will simply paint my bedroom. This time the colour shall do everything. By means of its simplicity it shall lend things a grand style, and shall suggest absolute peace and slumber... The walls are pale violet, the floor is covered with red tiles, the wood of the bed and of the chairs is a warm yellow, the sheets and the pillow are a light yellow-green, the quilt is scarlet, the window green, the washstand is orange, the wash-basin is blue, and the doors are mauve. That is all there is nothing more in the room... As there is no white in the picture, the frame should be white. This work will compensate me for the compulsory rest to which I have been condemned. ...Shadows and cast shadows are suppressed, and the colour is rendered in dull and distinct tones like crape of many colours.
** Letter to Theo, p. 31.
* I should like to make copies of "The Tarascon Diligence," "The Vineyard, "The Harvest," and "The Red Cabaret," especially of the night café, for its colouring is exceptionally characteristic. There is only one white figure in the middle which will have to be painted in afresh and improved in drawing, although it is good as far as its colour is concerned. The South really looks like this, I cannot help saying so. The whole scheme is a harmony in reddish green. I do not need to go to the Museum and to see Titian and Velasquez. I have studied my trade in Nature's workshop, and now I know better than I did before I took my little journey, what is above all necessary if one wishes to paint the South. Heavens! what fools all these painters are! They say that Delacroix does not paint the Orient as it is. Only Parisians—Gerome, etc.—can paint the Orient as it is—is that their claim? It really is a funny thing, this business of painting, out in the wind and the sun. ...[O]ne simply sets to like mad, as if the devil himself were at one's back, until the canvas is covered. It is precisely in this way that one discovers what everything depends upon. And this is the whole secret. ...[O]ne ...introduces something of one's own good cheer and laughter into it.
** Letter to Theo, p. 34.
* [I]nstead of reproducing exactly what I see before me, I treat the colouring in a perfectly arbitrary fashion. ...What I aim at above all is powerful expression. ...Just suppose that I am to paint the portrait of an artist friend—an artist who dreams great dreams and who works as the nightingale sings, simply because it it is his nature to do so. ...All the love I feel for him I should like to reveal in my painting ...To begin with ...I paint him just as he is, as faithfully as possible still this is only the beginning. ...Now I begin to apply the colour arbitrarily. I exaggerate the tone of his fair hair; I take orange, chrome, and dull lemon yellow. Behind his head, instead of the trivial wall of the room I paint infinity. I make a simple background out of the richest of blues, as strong as my palette will allow. And thus, owing to this simple combination, the fair and luminous head has the mysterious effect, upon the rich blue background, of a star suspended in dark ether. ...But one ought to picture this sort of fellow in the scorching noonday sun, in the midst of the harvest. Hence this flaming orange, like a red-hot iron; hence the luminous shadows like old gold. ...[W]e wish to show that this reading has become part of our flesh and blood. I can only choose between being a good and a bad painter. I choose the former.
** Letter to Theo, pp. 37-38.
* One cannot be at the Pole and at the Equator at once. One must choose one's way; at least this is what I hope to do, and my way will be the road to colour.
** Letter to Theo, p. 137.

### Interaction of Color (1963)

    by Joseph Albers
* Significantly, complementaries, though they are the basic color contrast or interval, are... quite vague. ...[T]he compliment of a specific color, when placed in different systems, will look different. ...[A] triad or tetrad of one system will hardly fit into another... [W]e may forget... those rules of thumb of complementaries... and of triads and tetrads... They are worn out.
* Good painting, good coloring, is comparable to good cooking. Even a good cooking recipe demands... repeated tasting... And the best tasting... depends on a cook with taste.
* By giving up preference for harmony, we accept dissonance to be as desirable as consonance.
* [T]he increase in amount of color... visually reduces distance. ...[I]t often produces nearness -- meaning intimacy -- and respect.

### The Psychology of Color and Design (1974)

    by Deborah T. Sharpe
* [A]pproximately 90 percent of the adult population is form dominant, color-dominant persons have been referred to as deviates. One of the most widely-held theories... states that since color is a primitive response, the adult color-dominant personality tends to be impulsive, immature, egocentric, and less intelligent... Other theories attribute greater creativity and flexibility to the color-dominant... [I]t is questionable how valid these tests can be in measuring intellectual ability...
* The Pfister Color Pyramid Test was given to evaluate the color preferences of feeble-minded grade school children; it was found that between the ages of six and thirteen there was little variation in... preferences, though a striking preference was noted for red as well as a negative correlation between red and intellectual functioning. Color-form perception measures of juvenile delinquents have consistently shown them to be a color-dominant group. ...[O]ther personality measures of this group... have found the delinquents to be controlled by their impulses and weak in ego strength.
* The complementary-harmony school of colorists is based primarily on specific color systems or concepts, namely, the Munsell color system and Itten's color circle, Ostwald's color system... uses a more subjective criterion... Harmony is in the eye of the beholder. Opposites on the Ostwald color circle will neither mix into grays nor lend themselves to afterimages... Complementary colors equal harmony equals balance, according to the traditional school... Noncomplementary colors equal assymetry equal tension, according to the modern school. But... these two frameworks do not take into consideration the eclectic approach, which utilizes neither... but, rather, is based on the demands of the space, subject matter, light, sequence of... applications and... interpretation of the overall tasks. ...[A] whole new generation of designers and colorists appears to have heard nothing of these rules. The increasing use of asymmetry... is creating a new design idiom.
* The concept of color harmony by the color wheel is an objective conclusion arrived at by intellectual activity. The response to color... is emotional; thus there is no guarantee that what is produced in an intellectual manner will be pleasing to the emotions. Man responds to form with his intellect and to color with his emotions; he can be said to survive by form and to live by color.

### The Physics and Chemistry of Color: The Fifteen Causes of Color (1983)

    by Kurt Nassau
* The blue dye indigo is one of the oldest dyes known to man, having been in use for more than 4000 years. Its preparation by complex extraction processes was described in Sanskrit writings, and it was used to dye Egyptian mummy cloth. When Julius Caesar invaded Britain in 55 B.C., he found that the local Picts ("painted people") decorated themselves with woad, a form of indigo. And who, today, does not know the all-pervading blue jeans, frequently dyed with the same indigo, now manufactured synthetically. While the transition metal colors... can be adequately explained by ligand field theory, the all-encompassing molecular orbital theory is required to explain the color of organic molecules. These include dyes and pigments, both as they occur in nature as colorants in the animal and vegetable kingdoms from which they were first extracted, and also as the triumphs of the synthetic dye industry which have displaced natural dyes almost completely. ...[W]e use the term "colorant" to include all types of organic dyes and pigments involving electrons on more than one atom in organic molecules, while multi-atom color-producing systems involving charge transfer are deferred ...
** Ch. 6 Color in Organic Molecules, p. 109.
* A crystal of corundum containing a few hundredths of one percent of titanium is colorless. If, instead it contains a similar amount of iron, a very pale yellow may be seen. If both impurities are present together, however, the result is a magnificent deep blue color, that of blue sapphire... The process at work is intervalence charge transfer, the motion of an electron from one transition metal to another produced by the absorption of light energy; this results in a temporary change in valence state of both ions. Such a mechanism is the cause of the blue sapphire and the black and dark colors of many transition metal oxides such as iron oxide magnetite Fe$_3$O$_4$. The mechanism is sometimes also called cooperative charge transfer. Somewhat analogous charge transfer processes also occur in ligand field situations; this can lead to color even if there are no unpaired electrons to cause the color by... transition mechanisms... [I]t is possible to describe many of the donor-acceptor dyes... as involving charge transfer, although... not commonly used.
** Ch. 7 Charge Transfer Color, p. 140.
* [S]emiconductors as silicon are distinct from metals, yet the properties of both are readily explained by the same band theory. ...[T]he semiconducting properties of this metalic-appearing silicon and the absence of color and insulating properties of, say, diamond, are both part of a continuous range of materials which unexpectedly includes the red, orange, and yellow colors of medium band-gap semiconductors. ...It is the delocalized nature of the valence electrons, their ability to move freely throughout a piece of metal or semiconductor, which is at the root of the characteristics of these two types of material.
** Ch. 8 Color in Metals and Semiconductors, p. 155.

## See also

* Art
* Chemistry
* Color Field
* Light
* Painting
* Physics
* Race
* Rainbows

## External links and sources

Color at Wikiquote's sister projects: :
* Article at Wikipedia
* Definitions and translations from Wiktionary
* Media from Commons
* Learning resources from Wikiversity
* News stories from Wikinews
* Source texts from Wikisource
* Textbooks from Wikibooks
* Travel guide from Wikivoyage
* Bibliography Database on Color Theory, Buenos Aires University
* Why Should Engineers and Scientists Be Worried About Color?
* Robert Ridgway's A Nomenclature of Colors (1886) and Color Standards and Color Nomenclature (1912) - text-searchable digital facsimiles at Linda Hall Library
* Albert Henry Munsell's A Color Notation, (1907) at Project Gutenberg
* AIC, International Colour Association
* The Effect of Color | OFF BOOK Documentary produced by Off Book (web series
* Study of the history of colors