How about those suede erasers? This is a light color and it’s inside, so might work too.
DISCLAIMER: I don't rehab so I don't know if this will do damage.
Would Mr. Clean magic eraser work?
I did try one of those Magic Erasers (not a Mr Clean brand, however). I was afraid to rub too hard, so I brushed it lightly over the whole pocket. I didn't see much improvement, maybe a bit of lightening overall. but the black smudges weren't affected.
I'm going to look for a suede eraser and see if it might help. Thanks for the suggestions!