Pink river dolphin

There are several hypotheses on why the Amazon river dolphins are pink.

An excerpt from the article 25 facts about pink river dolphin
One states their pink hue developed as a result of constant fighting with each other since their scar tissue is pink. Another theory states their blood veins are beneath their skin, and thus the color. Another hypothesis focuses on the fact that the pink hue allows them to camouflage against the red mud.