Countershading is the natural phenomenon of an animal having a darker upper half of its body, and a lighter lower half. Consider the pale stomach of the dolphin, the natural gradient of a common lizard, or the crunchy hide of the chicken fritta and its soft, white underbelly. See how this countershading flattens out the meat visually, making it difficult to spot?
Pictured here is Countershade, dark on top, light on the bottom - like I like my women. No, I do not know what I mean by that.