Preferably a high temperature enamel, legit soldermask stuff especially. Which isn't crazy or nasty, it's readily available, and sets with a UV LED flashlight.
Also polyimide tape, which is probably still too thick. Nail polish is fine if it doesn't melt under soldering heat, which... I'd be weary about. Try it, see if it makes a mess. It may go on too thick, straight from the bottle yeah, but that's easily fixed with a little solvent, e.g. acetone, ethyl acetate.

Spray paints of various sorts; maybe a high temperature one from the hardware store. Hm, beware of possible conductivity in black or metallic types I guess? Most should be ok though. Doesn't need to be the super temp enamel/ceramic kind, just something that doesn't melt as easily.
Tim