The reason why it is pink is that hippo secretes two kind of unique acids called “Hipposudoric acid” and “Norhipposudoric acid“. The two acids got their names from the word Hippopotamus.



The Hipposudoric acid is reddish in color and often known as, “Blood Sweat” (hipposudoric, referring to hippo sweat), although it s neither blood nor sweat. While the other, Norhipposudoric acid is bright orange. Both these acids are strong enough to minimize the growth of the bacteria on the Hippo’s skin. These acids also act as a sunscreen for the Hippo’s skin as they absorb the UV rays that destroy the skin cells. In a milking Hippo the two acids get combined with the white milk and thus pink colored milk is ejected. So the formula is simple:



White + Red = Pink



Hippos are the only mammals that produce pink milk; there were many who believed that Yak’s milk is also pink but the fact is that when a Yak gives birth to a calf, the first milk produced contains blood that gives it a pink color and is known by the name of “Beastings”. After some time the milk turns back to the usual white color.

http://en.wikipedia.org/wiki/Talk%3AHippopotamus