
Naomi: Because they love to eat shrimps.
What? You think this is a joke? I thought so too. I love to eat shrimps too, but last time I check I am slightly brown-- not pink! And aren't shrimps pink only after they're cooked?
Then we found in a science textbook and a few trusted source, such as this
wikipedia article, that perhaps this is not a joke after all. Flamingos are pink really because they eat lots of shrimps.