No, Michael Jackson's body is not black.
Michael Jackson has vitiligo, a record of his medical history was leaked on the net a while ago and it states that he does.
Vitiligo is a disease that kills skin pigmentations in your skin. Michael Jackson first found out about his disease in 1984. He is a performer and is regulary on TV and such. He needs to look good. So his personal doctor gave him a cream that evens out the colour of your skin.
Michael keeped using the cream, and as the white pigmentations in his skin grew larger, his skin turned lighter as a result of evening out the colour of his skin.
Now a-days, the people that are closest to him, claim that his skin is a grey-ish colour, so Michael cover's it up with make-up.