I've never tried this, but you might be able to use some of that bluing material used on the metal surfaces of firearms. Check with your local gun shop. If the color is close enough, you might be able to apply a tiny amount with a very fine brush just to hide the mark. I've used a regular old black marker before with excellent results. Good luck.
Darn it, I scratched my Roland Now what
For some stupid reason I was cleaning one of the shelves of my stero rack and a I accidently hit the top of the shelf with my Roland gear causing a nice scratch on the top plate. ( black ) Thanfully it is not to the metal but more of a good rub mark. This is ( was ) an expensive piece of equipment. Any ideas on how I could possibly remove this dreadful mark.