Pretty funny anyone asking me for advice on anything "artistic". The best way I can describe my abilities is: "I suck." (And that's on a good day.)
All I did was take one of these black Sharpies, hold the gun in my left hand and then try to color it in freehand with the sharpie as best I could "within the lines" so to speak. It's nothing to look at but it does help the contrast.
How durable it will prove to be remains to be seen but it takes literally a minute or two to reapply. (Not sure how brave I'd be with black paint but I'm sure it wouldn't be much harder.)