This is the dorsal view of the gras

This is the dorsal view of the grass frog. The skin on the dorsal side of the frog is dark to provide camouflage from potential predators. The patches of colour are the result of pigment cells called chromatophores.
Its skin is loosely held to the body and produces mucus secretions that keeps the skin from drying out and allows the frog to breathe. Some frogs (not grass frogs) have poison cells that produce bitter secretions that pass through the skin. This provides extra protection for the frog.
Since the frog breathes through its skin, the skin has a large number of blood vessels that aid in gas exchange.