Countershading

Most animals have lighter coloration on the belly than on the back. This form of camouflage, called countershading, disguises prey animals by offsetting the effects of shadowing on the bottom surfaces.

When standing in bright sunlight, this Cuvier's gazelle is likely to present an unexpected silhouette to a potential predator. 

Countershading is commonly seen in marine animals such as fish as well, darker on the dorsal surfaces and lighter on the ventral surfaces.

Since both predators and prey need to remain hidden, both are frequently countershaded. Penguins and killer whales evolved from very different terrestrial ancestors, and both developed a similar black and white pattern of countershading.

Thanks, Heidi Richter

Images from Wikipedia. Here's Wiki's article on Countershading

Countershading is mentioned in Imaginative Realism