Welcome to the world of rabbitfish!
Indeed they can be somewhat difficult to ID, like Delphinus I was on the quest for
Siganus doliatus Scribbled Rabbitfish and thought I had one when my order came in...unfortunately mine is what I believe to be a
Siganus argenteus which could eventually grow to 16"! The hard part with IDing is that they are masters of disguise and change colors and patterns as their moods suit them. Mine is often almost completely black, other times silver, or disguised as rock... This picture shows just a few of his "moods"
This is the same fish with some photos on the same day! Fascinating to watch as he can change his color and patterns almost instantly. This is why IDing from photos on the net can be tough.
Francis "Alberta-newb"