I purchased a Yellow Tail under the impression that they were less aggressive than other Damsels. He was very territorial, and I'm fairly certain that he killed my Ocellaris and a couple of my Chromis. Several mornings I woke up to dead or injured fish. Needless to say, the Yellow Tail is now in my friend's Puffer tank, and I haven't had any more problems since. If you're looking for a splash of blue, the Blue Reef Chromis has a nice color, without all of the aggression.