Feather coloration: Melanins and carotenoids
Feather coloration is due to two basic pigments known as melanins which are pigment granules of brown, black or yellow and the carotenoids which are either red or yellow. Green, blue and iridescent markings on sunbirds and other species are due to the peculiar surface and (Nectarinidae) internal structure of their feathers. Absence of pigments result in partial or complete albinism.

Scientists found that many bird feathers that have flourescent pigments are the same feathers used in courtship displays.
Photograph courtesy of Science