He's a black combtooth Blenny. I've got one. He just recently stripped all my green SPS corals bare.
Saltwater Aquarium Fish for Marine Aquariums: Black Combtooth Blenny
The only real color change mine does is the brite purple/blue lines that come out when he's upset. I've never seen any real color change on his tail. But each one is different in some way.
Clown you got it first I didn't look at your sicentific name. When I saw the picture I was 100% of the name I bought it under. Thanks all!