A permanent marker could be found that might match, you would need to test. Office Depot has a fairly nice selection to try. Make sure to test it somewhere that can't be seen on the gun ie. inside the magwell and wipe it off after a few seconds to see if it blends. You can't have it re-anodized as the frame is a soft cast metal and the rails have a hardening that is factory applied. Any dipping would remove that hardening treatment and make the gun a super wear machine with any fair amount of use.