IOW, it's not paint. As Avionic is saying, it's anodized.
That is, if we're talking about the faceplates.
The covers are just painted. For most vintage gear needing black paint, I prefer the Krylon Acryli-Quik Acrylic Lacquer. It's only available as a "commercial" product these days, but can be found on Amazon or at Grainger. The semi-flat is a dead ringer for JBL speaker baffles. Might be a shade too flat for the cases.
For minor touch-ups on the aluminum faceplates, I've always used Birchwood casey aluminum black. Clean the area extremely well with alcohol, then clean it again, and probably again. Dab a little on with a cotton swab (the pro swabs work best) a few times and it will all but disappear in most lighting conditions.