Basking shark

The basking shark's fat, large liver allows it to float in the water. It makes up about 25% of its body weight. 

An excerpt from the article 16 facts about Basking shark

The basking shark's body coloration is almost monochromatic - dark gray, gray-brown to black, with the back darker than the underside. There are often light or dark patches on the back, sides of the body and under the head.

The underside of the fins is also dark gray, but in juveniles the fins are white with a clear delineation of dark areas. In very rare cases, basking sharks can develop albinism.