So what you're working on, Thomas, is a feature of Skatter that
randomly replaces the default material in the component by a selected set of colors (thus getting rid of the mat id issue as per in vray, 3dsmax, maya, etc.) that you define in a specific skatter parameter or
randomly replaces a material with a specific UV defined (like textured material, which implies correct UV mapping / UV wrapping) by another set of textured materials, also defined by a specific skatter window
I think that 1. is way simpler as there are no UV issue involved (and could be achieved by using some already available ruby scripts), but 2. would be very powerful.
What you seemed to be working on (but I could be wrong ) is a vertex color based color variation feature (for leaves for instance), and this would be very impressive but I can't see how you'd do that, as it's very render engine specific.
And there's also the skatter id per material (be able to define skatter zones by sketchup materials, a kind of multi-sub mat alla sketchup+skatter), which would be very useful for landscaping, as we could use this to quickly define greenery species zones, as a cheap replacement the very awaited "random clusters" feature.