Why is flamingo pink?

Flamingos are not pink at birth. The chicks of these birds are gray-white and remain so until they begin to eat seafood and algae, which have a large amount of carotenoids. This substance, when consumed constantly by its flamingos, imparts a pink color to its plumage. And if its amount in the body is very large, then flamingos can be almost red in color.
But if the flamingo stops eating food that contains this substance, then gradually its color will return to gray-white.