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.
Nudibranchs, a type of sea slug, move slowly and spend a lot of time on top of what they’re eating, often sponges, algae, coral, and bright anemones, so incorporating the color of their prey into the nudibranchs’ bodies helps camouflage them while eating.
Cedar waxwings are songbirds whose tail tips are naturally yellow, but the red berries of the Morrow’s honeysuckle, which the birds find delicious, turns their tails orange.
The striking neck “cape” of the frill-necked lizard picks up colors from the food the reptile eats, which generally includes insects, smaller reptiles and mammals.
The brilliant yellow of the mature male American goldfinch is also obtained from pigments in his seedy, plant-y diet.