I actually just took my rainbow shark back to the LFS for a future trade to give it a better home. I had him for about 4 months. It's got something against the German Blue Rams, not to mention it chews half my plants off at the base. It's always been extremely active in the aquarium, but never really gave chase to anything. Since the Rams came in a couple weeks back, the shark would spend half the day terrorizing the Rams. Both the shark and the ram's lost their colour's showing stress. The Rainbow Shark was the most entertaining of my fish to watch beforehand, with the exception of my killifish. I told the LFS owner that if he hangs on to the shark for a couple weeks before putting it up for sale, it should get a lot of it's dark black back enabling him to sell it for a better price, given the size and brilliant red of it's fins. Once it sells, I get a store credit for part of what he gets for it. He's got it in a 70G with only a few other fish, so it should relex a bit (I hope). I'm in the LFS at least once a week to pick the owners brain (and go broke), so I'll kep checking on the shark to see how it's colour's are doing.
Colin