Posted By:
Steve FIf you're right, that's a cool error. It's shaped like a stain from here.
I'd bought a raw card, a 49 leaf that had similar staining when the collector tried to remove writing from the border (blue ink). Over saturation with acetone removed the the blue alright but also wicked into the red ink causing a similar effect.
I also have another somewhere, where a small spot of the red pass 'washed off' yet the yellow pass beneath remained. Like yours though, the front lithos were stained and the back inks appeared unharmed. Good luck