Value is the lightness or darkness of a color. Metamerism is when two objects with differing spectral curves match under a given illuminant. An example of this is a restoration that matches the tooth or adjacent teeth in the dental operatory, but when viewed in a different lighting condition, the restoration no longer matches. Color constancy refers to the apparent color change exhibited by a single color when the spectral distribution of the light source is changed or when the angle of illumination or viewing is changed. Each of these factors has its own variables, which if changed, the perception of color changes also.
Many persons have some sort of color blindness, often a red-green deficiency.
These deficiencies involve hue and chroma, but do not affect the perception of value. Some dentists may be able to compensate for a color-vision deficiency due to their ability to choose the correct value of a tooth. If shade selection is difficult for the color-deficient dentist, then use of auxiliary personnel is recommended for shade selection. Value, how light or how dark an object is, is the most important of the triad when initiating shade selection. An example of the importance of value for a tooth shade is to note a patient's response to a mismatched esthetic restoration.