Try using a felt tip marker that is made writing on CDRs.
How to touch up nicks on edge of black faceplate?
Black anodized faceplates on amps look nice but over time they tend to get little nicks on the edges that let the silver-colored metal show through. Do you have suggestions for how to touch up these little flaws? Sharpie won't do it -- has a slightly purple tint. I promise this is for my own use, not to try to hide any flaws on an object to sell!