damn, there's a really long thread on XDtalk about that topic
I used nail polish
trick is to get some kimwipes (think glass cleaner tissue), hoppes gun cleaner, and patience.
Let the nail polish dry, take the folded tissue and barely wet a corner, LIGHTLY rub on the surface, frequently changing to another corner. Get most of it off and reapply the nail polish. 3rd coat may or may not be needed. My gun's finish is not sensitive to acetone, ymmv, I take a tissue that is mostly dried from acetone and do a quick LIGHT wipe to get the last little bit of residue off.
Note: Gold Metal Flake is a B!TCH, crap got EVERYWHERE. SWMBO wanted it on her 22, unfortunately it got on my 22, it got on my XDM, got on my work bench. She loves the job on her 22 tho