Flamingos eat small crustaceans, algae, and other small animals that live in the water. These animals contain a pigment called carotenoid. Carotenoid is a red-orange pigment that is also found in carrots, tomatoes, and other fruits and vegetables.
When flamingos eat these animals, the carotenoid is absorbed into their bloodstream and deposited in their feathers. Over time, the carotenoid builds up and the feathers become pink.
The amount of carotenoid in a flamingo's diet will determine how pink its feathers are. Flamingos that eat a lot of carotenoid-rich foods will have brighter pink feathers than flamingos that eat less carotenoid.