What part of body of the frog help them to survive?

The upperside is more heavily pigmented than the underside witch is often white. You see distinctions of color etc, in animals which also use fast movement to avoid detection and predation. think of the logic of the adaptation in diurnal animals; fish for instance, when viewed from below are light bellied typically, so as to blend into the overhead intense light from the sun. when viewed from above, they are typically darker and mottled, to blend in with the darkening backround. Size doesn't matter. Look at the white shark or an orca. Same logic..