countershading

Countershading is a form of concealing coloration found in animals. It involves having the upper surfaces of the body more darkly pigmented than the lower, unilluminated areas. This coloration strategy helps to create a more uniform darkness across the animal's body, reducing the appearance of depth and shadows.12

This adaptation serves to mask the animal's form, making it harder for predators to spot or for prey to detect it. It is often superimposed over other forms of camouflage, like disruptive coloration. Many deepwater fish utilize a unique form of countershading with light-producing organs called photophores along their lower sides, which help to obliterate their silhouette when viewed from below in the dim light of the ocean depths. The first known use of the term "countershading" dates back to 1896.23