I don't think it is a chromis, because of the depth of the body. It is a damsel though, possibly a Pomacentrus Amboinensis, which has a common name of Yellow Damselfish. They are known to have a hint of purple or dark blue starting at the head and working its way down the dorsal fin. I may be wrong though... there are so many specie of damsel, that it is hard to identify some of them, especially when they are close to full grown, because of changes throughout its life. Young fish tend to be colorful and more drab when older. This is not always the case either...I guess with all the searching I did, I have to honestly say, I don't know. It just looks like some pictures I saw...