I know what the fish looks like, I have a pair myself.
I just think with the lighter background it will be harder to spot flukes, if they were there, than, say on a raccoon butterfly or something darker overall. But if you've had him a month and not noticed any opaque spots on the body or eyes then maybe it's not flukes, hopefully it's not.
Butterflies in general are very fussy eaters so it just takes them a while to get used to the idea of what you offer being "actual food". He should come around. Both mine eat flake and pellets as well as frozen (and aiptasia and majano .. and .. um .. blastomussa's, bubble corals, acan's, open brains .. any manner of SPS ..
gorgonians .. byssal glands of clams .. zoanthids .. palythoa's ... you name it!! .. unfortunately not a reef safe fish by any means! But they are the first butterfly I've attempted {have tried several others} that readily adapted to dry food like pellets and flakes). So my guess is yours will eventually warm up to what you offer. Have you tried clam on the half shell yet? He might go for that if you're worried he's not getting enough.