Is there something wrong with my Dogface Puffer?

[DHouse]

I purchased a Dogface puffer in august, Pic #1. After a week he changed into pic #2. I have been told that he is stressed, that he is sick and that he'll probably die soon. 7 months later, he is still black and he definitely is not stressed. He eats like a horse and will come to the top of the water and he lets me pet him. Has anyone else hade a dogface that changed like this?

Thanks in advance!

 

[fishguy242]

Hi,welcome to the reef, do you see any problems ?
looks a little on the thin side to me ?