The colours of a bird's feathers can be brought about by two different ways; (a) in a chemical way, in the form of pigmentation, which thus gives pigmentary colours or, (b) by the physical nature of the reflecting surface to give structural colours. Some colours can be due to a combination of these two methods. Pigmentary colours are not only used in feathers, but also in the bill and 'soft parts' like the skin. The commonest pigment in birds is melanin of which a few different types exist, giving a black (very common), brown, red-brown or yellow colour. Black melanin occurs in many black-coloured birds like the common Blackbird and Crow, and yellow melanin is for example responsible for the yellow colour of the down in domestic chicks. Another group of pigments, the carotenoids, is used for many red and orange feathers. Birds are unable to synthesize carotenoids themselves and obtain them (directly or indirectly) from plants and deposit them selectively in some tissues. Beside these two regularly used pigments, many others exist like protoporphyrin which occurs in the egg-shells of many birds. Structural colours are due either to interference, giving iridescent (metallic-like) colours that change with the angle of view (as in soap bubbles), or to the scattering of light giving non-iridescent structural colours. The structure responsible for iridescense is present in the barbules (see 'feather(s)') which in this case have a special torsion, accompanied by the loss of hooklets and flanges, reducing the mechanical strength of the vane. Consequently fully iridescent colours are not found in flight feathers. Some iridescent colours are brought about with the help of specially arranged melanin granules in the barbules (beside the 'normal' interference in the outer layer of barbule keratin). Non-iridescent structural colours (not changing with the angle of vision) are produced by the scattering of the shorter waves (yellow-green to blue) in white light by very small particles or air-filled cavities in the barbs of the feathers. This is especially useful for producing blue and green colours. Some colours can only be made by the combined action of two or more pigments, or of pigment and structure. For example the green colour of feathers is often the result of a yellow pigment plus non-iridescent scattering, while purple results from a red pigment plus scattering, and olive-green from the juxtaposition of tiny spots of black and yellow pigment. Finally, some birds colour their plumage with coloured secretions from the preen (or oil) gland, like the Great Indian Hornbill. This is called cosmetic coloration.

Alternative forms for colour : color, melanin, pigment.