Discolored Leather Rear Headrests
 

Help! I have an 02 Camry with leather interior. The leather interior was modified from fabric interior by the Toyota dealership when I bought the car in 09. So, the leather isn't that old. In the past month I've seen some wierd discoloration happening on both rear headrests. Those headrests are basically untouched by anyone's hands or heads because I rarely have backseat passengers. I'm attaching a photo. This stuff will not come off. When I touch it, it is not raised, it does not smear or scrape off. The strangest part is that it's rapidly getting worse. It's much worse this week than it was last week. I've asked a buddy that does mobile detailing work and he had no clue what it was.
I'm really hoping that it is not sun damage. I have no tint on my windows.
Any help would be greatly appreciated!!!!

You have the early stage of what I have on my 2009 beige rear seats. Any idea what this is?