Hello Harman, I believe that you can utilize a chemical/electrical cleaning system. Can't remember the manufacturer, however, it utilizes an electrical box of some sort and a ground clip and a holder that has a sponge attached to it that you dip into a chemical solution and then wipe it over the spots that you are speaking of. I am sure others can provide a specific manufacturer and name for this process, sorry I can't remember it right now. Good luck and best regards, Allan
Electro-chemical cleaning, or something along those lines.
We have a surfox unit at work, uses a phosphoric acid mixture and a (reletivly) low level current with a pad covered tungsten electrode. Both pad and tungsten wear out after a while, pads first. It's supposed to be able to polish and etch logos and such but we just use it to remove oxide's.
I have also seen a "tigbrush" or something along those lines in person before. It used carbon fiber bristles and a similar amount of current and another phosphoric acid mixture. It worked a Lot faster but produced a slightly nasty smoke... wouldn't want to deal with that for any length of time without some forced air ventilation.
Either unit will take the color away if thats all you're after.