You Are (in some species, the color of) What You Eat
Newborn flamingos have grey feathers, but get pink by eating brine shrimp. These shrimp are full of carotenoids, which they get from the tiny algae they eat, and the flamingos break down carotenoids in their liver and deposit the compounds as orange and pink pigment throughout the bird’s body.
Salmon flesh also gets that salmon color from the tiny algae-eating crustaceans in their diet.
Those fishy carotenoids don’t just make things orangy-pink, though. The strikingly blue and large feet of the blue-footed booby also comes from these compounds in the bird’s seafood diet.