I think that flamingos are pink because they eat shrimp and algae. Flamingos are born a grayish color and have the appearance of being pink due to their diet which is high in beta carotene. They eat brine shrimp, blue green algae and other crustaceans.
Flamingos turn more pink as they grow. If a flamingo has a diet that does not consist of enough beta carotene then their color would turn back to a dull gray one, which can happen if their environment would change and crustaceans like brine shrimp and algae would no longer grow.
Flamingos do not necessarily need a rich beta carotene diet to survive, however it does create their beautiful bright pink plumage for which they are known. Contrary to beliefs they would not turn another color (besides gray) if their diet lacks this nutrient.
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