This sounds like one of those "impossible" requests, but I do wonder just how impossible it would really be. If something like this were created, I would imagine it would be some kind of script that would make only one poly of a brick get painted, or one "side". That would make things difficult, because if you just wanted to paint an entire brick another color, you would have to paint each side. Not to mention round bricks, which I think use 9 polys on the sides to create a round appearance.
But I'd certainly be willing to put in that effort, if it's for the sake of my build. :<