Repeated studies suggest that plumage color is linked to diet. Flamingos are famously pink because they extract pigments from the algae and crustaceans they eat. When deprived of their pinkish diet, the colorful feathers fade to white. This link between diet and color is not so clear when it comes to birds that are blue. Rather than being painted with pigments, blue is a “structural color.” Dehydrated fibers of keratin and pockets of air form a structural pattern that scatters white light in a way that causes the yellow and red wavelengths to cancel each other out. So unlike the red pigments that are deposited directly into flamboyant feathers, blue is only blue when the bird is in white light.

Fields, Helen. "Why Are Some Feathers Blue?" Smithsonian. Smithsonian.com, Mar. 2012. Web. 12 Jan. 2015.