Interesting Note:  Frogs in the family Centrolenidae are commonly referred to as "Glass Frogs" as they all have clear, glass-like skin on their abdomen and legs.  Scientists were originally baffled as to how clear stomachs and legs would work as effective camouflage when their back was still opaque until realizing that the clear legs softens the frog's silhouette on the leaves, creating a sort of artificial gradient from the leaf's color to their back's markings.  This optical illusion turned out to be more than enough to hide them from most birds seeking a snack.