In Nature, colour may be a source of great beauty to the beholder, but to a plant or an animal it is most often a means of survival. . . . Natural colour arises from a diversity of mechanisms, often associated with distinct functions. Dyes and stains are used by many creatures, frequently for camouflage. Structural colourtypified by the metallic sheen of a Mallard ducks blue speculumis generally used for the intense colours that announce the presence of an individual, as for example in a mating display. Colour can also be used for warning, as in the poisonous fire-bellied toad, or even for mimicry. Less commonly, animals can dispense with colour altogether and become transparent, or, as in the squid, they can actively control skin colour for the purpose of camouflage, or for attraction and mating.

—Trevor Lamb and Janine Bourriau, from the introduction to Colour: Art & Science, edited by Trevor Lamb and Janine Bourriau, 1995.