Countershading, or Thayer's Law, is a form of camouflage. Countershading is the pattern of animal coloration in which an animal’s pigmentation is darker on the upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptiles, birds, and fish, and has existed since at least the Cretaceous period.

Countershading, or Thayer's Law, is a form of camouflage. Countershading is the pattern of animal coloration in which an animal’s pigmentation is darker on the upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptiles, birds, and fish, and has existed since at least the Cretaceous period.