You can get into the overseeding market pretty well as long as it is for dormant Bermuda lawns. Keep away from overseeding high dollar Zoysia!!
As far as lawn painting.........it is touch and go.......or better yet iffy!! In my area, only a handful of commercial properties will pay for spraying dormant turf green for the winter season. The Zoysia lawns look awesome and hold the color well but the Bermuda's growth characteristics makes it harder to paint and get a sustained color. You end up overspraying and getting the soil green as well. It has a tendency of fading and being sparse.