My LFS occasionally gets swamp darters in their feeder tanks. They put them in their plant tank sometimes, and the ones in there are bright green. I found one in a tank with a bunch of bottom-hugging rosy reds (it was cold out and they could apparently sense it), and he was exactly the same color as the rosy reds. I only recognized him because he hopped like a darter. He's in my tank now, and he's nearly pure black. I know all darters and most cryptic fish have some color change abilities, but I've seen a LOT of colors in swamp darters. Tan, white, yellowish, light brown, medium brown (how they usually look), dark brown, black, and two shades of green. I'm tempted to put this guy in a tank with some aluminum foil or something and see if he goes all silver. Or maybe even over something red- I bet he could go at least reddish-brown.
Anyone seen these guys turn red or silver? Any other cool colors?