Now that's interesting.
One of the bright reds used at the time, was cochineal, which is water soluble.
I'm thinking the water plus some heat or chemical, or very long immersion allows the cochineal dye to be partly dissolved and once dissolved it migrates.
https://en.wikipedia.org/wiki/Cochineal
Madder/Alizarin is only slightly water soluble.
The card that left parts of its front and maybe that red impression/stain was probably Carrigan (Almost certainly since part of "Boston" is visible and Carrigan was the only Red Sox player with a red background)