I would really think it out, many of them look great as is...
I had a 7,5cm KwK 40 case that I got long ago that was water recovered, copper washed steel. It was heavily pitted along one side and moderately pitted the rest of the way...
I was young and dumb and impatient, did a crappy job with some body filler (lumpy, not well done!) and sprayed it with Testors brass metallic paint. Looked OK, but I never liked it. Picked up a much nicer one, so decided to really work on the old one.
Sanded all the old paint off of it, and the body filler until all was smooth (but still a lot of uneveness and pits), went over it with body filler again, block sanded it, body filler, sand, body filler, sand...finally did a coat of sandable primer, wet sanded, then went to an auto parts store where they have a ton of good, automotive color match metallic colors. I decided to go with a steel case color.
Here is a before photo, while working on it, the final product, then complete with a Milcorem resin 7,5cm PzGr projectile. Needs to be re-stenciled but you get the idea. These Milcorem projectiles are fantastic!
Take a look at the selection of auto color match metallics in spray cans, might be perfect...