We spend a lot of time looking for junco nests in my field work, which means we spend a lot of time looking at the ground, which means we see a lot of these little guys:
Pacific tree frogs come in two main flavors: brown and green.
Some frogs stay the same color for their entire lives, but some can change from brown to green, or vice versa, depending on whether the background is dark (brown) or light (green). You can see how this might be handy if you want to blend in with the background.
You can’t see me!
Tough Little Birds 