David is right on with the black & white stuffed cats. I'd say add a middle color gray or brown too. Looking at the photos you posted, it looks like you are most of the way there as far as stuffed kitties go.

This is also known as the "Teddy Bear Test" which was largely popularized by Moose Peterson. If you really want good test subjects, get the ones with marble eyes rather than plastic. It will give you a better idea of how to work with catch lights and such later on.