It’s such a small amount that I hadn’t really paid it any attention, until I took the photos. It could just be discoloration from rubbing up against pocket lint and other items. I may try a little alcohol to clean it and see if it’s just surface, or if it goes deeper. I do have some Instamorph that I used to repair the hardware of a metal basket that attaches to a pole, over a year ago. It has not discolored at all.
When the original stylus broke off, it revealed a hole that the ballpoint tip would stick through. So I had to plug it with something. The Instamorph has worked great, in that it hasn’t deformed or eroded. It creates a really good seal. When attempting to pull off the cap, there’s a little extra suction resistance, so it actually “pops” a bit when finally pulled off.