That is an Atlantic Blue Tang. They are yellow as juvies and then turn darker and darker blue as they age. Some develope a yellow spot on them. Here is a picture of the juvy that I had that got stuck under a rock and died.
I am waiting for this web site to get some back in stock to get a new one. Great fish.
I just added a small ABT to my tank today. Its about the size of a golfball and looks more like the Avitar that JnJ has.
They had two others at the LFS about the same size. They all had different coloring.