I should begin by saying that I just spent over 30 minutes reading through the thread about using hydrogen peroxide and sunlight to remove yellow discoloration. I will probably try that out at some point, but I'm a bit more concerned with causing/preventing it in the first place. I moved into a townhouse last October. When we got here, all the TF's went into a deep closet, and I wasn't able to finally unpack them until a few days ago. When I did, several white TF's had yellow plastic that I didn't remember them having, and those that did have some yellow before October looked much worse than I remembered. A few words about where and how they've been stored: - They've been in total darkness the entire time - The closet they're in is in the coldest room in the house - Each figure is in a sealed Ziploc bag, which is inside a sealed plastic bin - When we moved in October, the TF's were moved in the early evening time, at a time when the sun was almost completely down (i.e. they didn't bake inside a hot truck for hours on end) - Also, my wife and I do not smoke Is there an X factor I'm missing that could be causing it? Anybody have any thoughts at all?