On TheBlackParrot's server he changed the projectile of the spraypaint can to guns, it worked, he also changed the range of the paint projectile so you could paint stuff from far away, it's extremely possible to make a paintball gun, the only problems would be trust, wether something can be painted or not.
This brings me back to Miked Paintball game on Roblox, how it was very fine and worked like a charm. I would love to see this work.