Looks like some PNG gamma correction problems. I'm guessing that JJ has probably modified his monitor gamma, and whatever program he is using to make pixel art with is sophisticated enough to notice, and modify the gamma correction value. Something like that.
Anyway, I like the piece, especially the angularity. However, I wouldn't go overboard with that idea and try and make everything totally angular. I personally think that the angularity of everything works well with the organic forms of the body.