I may have to run for serious cover after I say this..............but I saw a show last week where a darling little (African/American) boy was afraid that he would be taken away from his Mom becuase she had turned white.
He was crying, and explained that people made fun of her and said she couldn't be his Mom and that he better find his real Mom, etc. It turns out that she suffered from a condition called Vitiligo, where the complexion (pigment) of dark-skinned people turns what looks to be Caucasian.
He had a picture of her when she was "normal" and then she came on camera---looking as "white" as can be. I've also heard MJ say that he suffers from this condition, and I can see how this could happen.
I was in the grocery store (with my kids whe they were small) and there was a man who had the appearance of a Pinto pony---very white skin and very dark skin. My kids were staring and talking LOUD and I went to another part of the store to avoid a problem (plus when they asked me what happened to him- I had no idea). I found out later that this condition is not at all uncommon in blacks, and so they said on that show recently.
I have seen quite a few more with this condition over the years, and I've seen people with varying stages of it. I see no reason to disbelieve MJ's explanantion of his "whitening". Also, these folks are not supposed to be in the sun---and that's why MJ carries an umbrella everywhere and tries to go out only at night.