Sorry - from just the one photo, and at that angle, I just found it difficult to tell whether he was pure or mixed. No offence intended

And even if his black mask ends just a little prematurely, it IS present!
Actually, on closer inspection of the photo, it looks just a little as though he's squinting with his left eye. That's the one that appears to have an unpigmented haw. Obviously, I'm still just looking at a photo and it could be for any reason, but I wonder about a touch of conjunctivitis? If so, eye drops would clear it up. That's maybe something you could get your vet to look at when you take him for his next set of shots.