 Countershading uses graded colour to counteract the effect of self @-@ shadowing , creating an illusion of flatness . Self @-@ shadowing makes an animal appear darker below than on top , grading from light to dark ; countershading ' paints in ' tones which are darkest on top , lightest below , making the countershaded animal nearly invisible against a suitable background . Thayer observed that " Animals are painted by Nature , darkest on those parts which tend to be most lighted by the sky 's light , and vice versa " . Accordingly , the principle of countershading is sometimes called Thayer 's Law . Countershading is widely used by terrestrial animals , such as gazelles and grasshoppers ; marine animals , such as sharks and dolphins ; and birds , such as snipe and dunlin . 
