Summary
Beta-carotene in shrimp colors their feathers. That"s why zoo flamingos often look pale.
Flamingo chicks are born gray-white. Pink color comes entirely from diet and takes years.
Beta-carotene from shrimp and algae is digested and deposited in feathers and skin. Without enough pigment, their color fades.
Color intensity matters for mate selection - bright pink means healthy and well-fed.
Bonus: Flamingo milk is also pink!
Source: Ornithology Journal