Im a black man but the top of my iris is gray?

I would see my optician. There are many disease that can play a factor. It can be Glaucoma. Glaucoma is an eye disorder in which the optic nerve suffers damage, permanently impacting vision in the affected area and progressing to complete blindness if untreated. It usually occurs when the fluid pressure in your eye increases. It can also be some kind of corneal disease. I would strongly recommend that you see your doctor. I hope the best for you :). Don't mean to scare you or anything, but I would get that examined.