Lejuan
Super Freak
I've noticed a strange trend with mine. I have a few Mark suits on display on shelves and they have not faded.
The other few Mark suits I have that are MISB have ALL faded. I wonder if it's the damn moisture packet behind the figures that has some sort of chemical reaction with the rubber/paint.
I'm making this assumption that it could be the culprit since none of my fresh air exposed displayed figures have ever encountered fading.
Now that is an interesting observation that I wish I was smart enough to explain. It does suggest that the paint fade - at least in your case - is not a symptom of UV exposure... who'd have thought it.