IMHO what a weapon looks like is unimportant, unless you want it to look more or less intimidating. However, I do often paint my rifles, not to much for camoflage, but because a black stock left in the sun can be painful to put on your cheek, think about your car's steering wheel in the summer. I know here in Phoenix, my old car, which had no tinting at all, the steering wheel would be too hot to touch in the summer. Same happened with my rifles.
So I would go with not black.