Craft stores like Michaels sell very fine tipped pens with silver and gold colors. I use these frequently for fine detail and have never had a problem with them hurting paint underneath.
Yeah, the black, thicker markers do have a purple cast, but that is an interesting patina for special uses. Don't use it a lot, but have used it in small amounts on "burned or overheated metal."
I also keep a very fine point white marker for spots where I need a very fine white line. This stuff does not cover well, but I can make a more uniform line than my other alternative, the "toothpick point" paint brush.