Another solution I have used (though not recently) is actual nail polish.

NOT "remover!" If you read the word "remover" in the first sentence, it's not there....and your mind must have filled it in...

Actual nail polish. (I'd choose something clear just to be safe, but try the experiment with whatever wife or girlfriend or mom or you have on hand. Obviously, ask permission first if it doesn't belong to you... )

Carefully apply a drop to the area you want to remove. Wait a few seconds then wipe off with an old rag or paper towel.

I have successfully removed a Storm Shadow v1 Cobra mark and the camo from Tunnel Rat v1's arms and face with this technique.

Also, after painting a Hot Wheels car a different color, my brother and I were able to get back to the base coat with this color. It seems to penetrate down only to the top layer.

Hope that helps!

As with all cutomizing, it's not an exact science. Please be careful and always use such products with adequate ventilation.