Texturing/UV help

So I've created a wheel for a monster truck; (see below) you'll notice that it's all black (rim and tyre) - the inner rim is meant to be grey and the outer beadlocks are meant to be purple. I have no idea how to convert from the basic non-texture materials I have applied to a texture atlas (which is what Besiege appears to use). At the moment I've just chucked a simple 2x2 pixel black bitmap in the skin pack's folder to achieve what I have below.

I don't really know Blender at all (most of the geometry was done in Sketchup and C4D, although I did use blender to fix the phong shading (which C4D didn't export for some reason)), so if someone could lay this out in simple terms for a complete n00b that would be cool.