Some pointers;
Indeed, the difference in the more angular fins, the dorsal (the top fin) and the anal (the bottom) fin, helps to separate the Ctenochaetus genus (Kole, Tomini) from the Acanthurus genus (Powder Blue, Atlantic Blue, Sohal, etc) which have rounded fin tips.
In the Ctenochaetus genus, this particular fish has two very distictive marking above and below his caudal fin (tail fin), two black dots. Only 3 Ctenochaetus have these markings, Chevrons, Blue-Eyed, and Tomini. It's pretty easy to eliminated two of those. It's not a Chevron due the striping pattern, nor does it have blue eyes. That leaves Tomini, which I believe this fish to be. If you notice on the dorsal, you can see the color pattern of a Tomini, granted, heavily faded.
The thing to not get hung up on, is the color. Tangs quite easily stress, and one of the results potentially is a drastic color change. Some tangs, such as a Naso, can change both directions, get really dark or change really light. I believe since this Tomini was only introduced today, it's still greatly stressed, and as the days go by, you'll start to see him color up.
