The problem is more that the pictures you'll find of S. ahli are also usually S. fryeri in the first place. It's EXTREMELY unlikely you have S. ahli. The pictures don't really give enough detail to be able to see how crisp the markings are, if there's white on the forehead, or if there's just red in the finnage, or actually on the body. There are a good number of very blue peacocks. Try to get another shot of the fish from directly side on, if you can.
Barbie