Here's a way I found. I have posted it in other places, but it's worth looking at again.
Using Fiberglass/Foam Sandwich Composite
If you are going for a truely simple shape, there would be no need for a mold, just some dimensions for cutting some 1" pink or blue Styrofoam insulation. I would think materials of fiberglass sheet (or similar) and epoxy (or resin) should work fine. I have heard that you get black color by mixing graphite powder with the epoxy (or resin) and there are liquid dyes that will turn it white (or probably a whole host of other colors). Enjoy!