MJ did use to paint his skin brown. He had vitiligo since he was a kid. But you keep loosing melanin as you age, so eventually there were so many white splotches, it became more convenient to match the color with the splotches.
The other major problem with painting too much of your skin is that it is very easy to start sweating and have the paint run off. This happened to MJ during concerts and there are pictures of it happening from the early 80s.
Eventually he bit the bullet and just bleached his skin. A lot of people with that advanced vitiligo end up making his decision for cosmetic reasons and convenience.
"But who prays for Satan? Who, in eighteen centuries, has had the common humanity to pray for the one sinner that needed it most?"
-Mark Twain