The third Little Pigment is called anthocyanin.
The anthocyanins are responsible for some of the most beautiful of the autumnal colours – reds, purples and even blues. The fiery red of maple leaves in the fall is due to the anthocyanin cyanidin. That glass of red wine is an aqueous solution of anthocyanin (plus, of course, some other fun stuff like alcohol, fragrances, flavours and so on).
Anthocyanins are members of an extensive and diverse group of plant chemicals called phenolics. Some phenolics are not themselves coloured but act as optical brighteners to enhance the colours of other pigments – as happens, for example, in the glowing golden autumn foliage of the Ginkgo tree. Another phenolic active in senescence is salicylic acid. It seems to have many jobs in plant development and stress response; so many in fact that its pain-relieving properties (in the form of aspirin) are frequently needed by researchers for whom sorting out its functions is a real headache.
Phenolic pigments are effective sunblockers, guarding plant cells from the harmful effect of too much light. They are believed to have health benefits in the human diet because of their antioxidant properties.
Anthocyanins and other phenolics, unlike carotenoids and chlorophylls, are generally quite water-soluble and this is reflected in where they live in the plant cell – not in the plastid, which is too hydrophobic, but in the wet environment of the vacuole. Thus the family histories of the Three Little Pigments – chlorophylls, carotenoids and anthocyanins – present a window on the state and interaction of the major organelles of plant cells as they develop, senesce, ripen and die.