[Bridwell]

A few years ago I bought a bunch of T206's that were glued to an old calendar from 1910. Since some were in poor shape anyways, I tried some different chemicals to soak them off of the backboard and remove the glue residue. One card with a yellow-orange background turned pink similar to the samples you guys are showing in your scans. The one I had, the colors of the player and his uniform weren't affected, only the background color.

I've also seen some cards where they had been glued in an album and the glue had affected the color right through the card to the front.