[GeeTwo]

We have used white paint in the past, but not spray paint. The big problem with paint is that most of the recommended bumper fabrics are nylon or other artificial fiber that do not take most paints well; they tend to flake or peel. If you want to do this, Try painting a scrap of fabric, letting it dry, then striking it against another piece of fabric, polycarbonate, and other surfaces likely to be encountered on the field a few dozen times. You probably will not be happy with the results.

Many t-shirt shops can provide iron-on numbers, or you can order them on-line from AndyMark, RoboPromo, or probably a variety of other vendors. Some teams make their own heat-applied numbers, but I don't know their recipes. Teams (not mine) have also reported having their numbers silk-screened and seemed happy with the results.