I've heard that hippo milk is pink.
Is this true?
And if it is, why?

I think this is an Internet legend that is oft repeated but without any evidence for it that I can find.

It is true that hippos secrete a red pigment in their sweat that acts as a natural suntan lotion (see URL below), but nowhere can i find evidence it is secreted in breast milk and thus turns it pink. Further, since the pigment is acidic I would guess that would not combine well with the milk.