Light has color components collectively known as the spectrum. The spectrum consists of red, orange, yellow, green, blue, indigo, and violet. The green light portion of the spectrum is not effectively absorbed by chlorophyll in plants. The green light is either reflected by or passed through the leaf. This is why leaves generally appear green.
Carotenoids represent a collection of two groups of pigments, carotenes, and xanthophylls.
Xanthophylls are yellow pigment responsible for the coloration found in dandelions, sunflowers, corn, egg yolks, and yellow leaves. In addition to carotenes and xanthophylls, three other chemical pigments play a role in foliage coloration. Anthocyanins produce blue, red, and violet colors. If the plant cell fluid is acidic, the coloration will be red. Conversely, if the fluid is basic, then the color will be blue.