Some months back I saw another one in with a sea of little yellow things that looked identical otherwise, but now I think that was actually two different types that happen to look the same as youngsters (after all, my yellow damsel that I now think is Pomacentrus sp. started out looking just like that - very different from the adult shape and caused me to mis-ID as a result). However, I was lucky today and I might have actually found the answer. One store I happened to stop by today got in a shipment of just these little blue fish that actually contained some more mature individuals, including perfect gradient from exactly what mine looks like to what the larger ones should look like with intermediate examples (maybe mine is stunted from a hard early life? No idea). The larger ones actually looked to be Amblyglyphidodon curacao based on the stripes, which was not what I was expecting really. There were enough intermediate stages present in the group though that I have no doubt I was seeing the same species from small to large. It may be that there are some color forms within that; some of the little blue guys had yellow showing, but others had absolutely none. So, it could still be some color morph stuff going on.