For a painted finish, friends of mine have had Walter Birsong's
Black-T finish put on and generally feel they're very good and perhaps the best of the painted finishes for a combination of protection and dry lubrication. They eventually get small points of holster wear at the edges of carry guns that they practice presentations with, but all the painted-on finishes do that in the long run. So do black oxide, bluing, or Parkerizing for that matter.
If you don't want any wear you are going to have to get one of the finishes Bill suggested, and they limit your color choices. When nitriding, a plasma oxidation final step gives a black finish that adds corrosion resistance same as black oxide or bluing does. You want to examine samples of any process for appearance before deciding.