It surely can't be as easy as simply spray painting it because i imagine that would flake and peel pretty fast.
Actually, it does not.
Just do a Google search on "Krylon Camo" paint jobs for rifles...
Easy to do, easy to touch-up, easy to remove and do-over if the mood strikes, and actually fairly durable when properly clear-coated with Matte clear coat.
Not to mention, a ton of fun to do yourself...