alot of corals can harm other if put too close ,,chemical warfare as stated.. also anemones etc.. i knwo that clown gobies and others of their family are bad for sps because they nest in them but that cause dead spots not color to be thrown off.. same with the corals, if your color is off its either 1. lighting or 2. levels IMO .. other than that if they are surviving and have good polyp extension i dont see another problem