Well it’s no surprise that you can touch up black paint with a black permanent marker, but here is a little use I found recently to be of help with something worn looking.
The black zipper on a small bag of mine was looking—eh, chipped and faded. But I still wanted to use the bag. How to make it look better?
I remembered using a black sharpie to blend a silver screw into a black metal bracket once. So I tried it on this metal zipper. (I wouldn’t try doing this on anything expensive).
The black is not a perfect match, but from a distance it just sort of blends in, so the fact that the zipper is worn is not really noticeable. I might be looking for other little things to touch up now.