Yes, I TOTALLY believe Michael has vitiligo.

As megola82 said very well, you can actually see the blotches on his skin on many photos and even videos, even though they try to cover them up with makeup.

That's why he can't be exposed to the sun too long, and many times when he's outdoors you'll see he tries to cover his skin with an umbrella or clothes with long sleeves, etc.

Poor MJ, I know it's a big hassle for him to have to deal with that, PLUS the peole that don't believe him and think he's actually that pale on purpose...:-(