People always ask me how I paint my firearms, and what paint do I use. Personally I have only used Krylon brand Camo line paints. These paints are relatively cheap, provide a thin protective layer, and the camo pattern can be changed for very little cost. Painting My Buddies Firearm Video
The paint can be easily applied by just spraying it on, by a sponge, by taping the firearm and spraying on a pattern, or by using local vegetation to provide your patterns. I suggest you use very light coats so that you do not have heavy build ups that can trap water and eventually cause rust. Less is really more in this aspect of applying the paint. The time in between coats should be at least thirty seconds to one minute to give the first color a chance to solidify so that you don’t have heavy build ups. You can re-apply the paint at any time with little or no peeling or chipping. Some people suggest stripping the weapon of oil first, but I have never done that with fair to good results. All my firearms are treated with frog lube over the paint. I had a personal friend put clear dura coat over some krylon with a pretty cool effect. Dura Coat over Krylon Video
You can supplement your paint with things like colored furniture and Camo-Form tape from McNett. I paint the majority of my long guns, and none of my pistols. I would probably not paint a home defense gun solely because I wouldn’t want them holding a painted tacticool gun up in court and having the jurors collectively sucking the air out of the room when they gasp at how bad ass it is or by how shocked they are because they are ignorant sheep. There really is no reason to paint your home defense firearm anyway unless your painting it grey or something non nondescript. Whatever firearm you do choose to paint DO NOT paint the bolt or any type of operating arms or parts.
In the long run it is up to you how and why you paint your firearms, but I prefer not to be carrying around a big black boom stick in the desert that screams “Look at me! I have a gun!”