I did further research on this 'cause with all the conflicting opinions I began to think maybe I was wrong. See the faint white line on the base of the dorsal fin, the yellow pectoral fins, the faint white bar on the base of the tail fin and the blue around the caudal (sp?) peduncle, and the faint yellow on the face between the eyes.
Definitely a yellow fin or yellowmask. Acanthurus xanthopterus. This fish will turn into a striking adult fish. How big is your tank? The Point Defiance Zoo in Tacoma, WA has 3 large adults. They constantly school together and are awesome in appearance.