I’ve been thinking about the textures alot even though I’m not a texturer so here are my thoughts.
Orange could be a different material from the Grays, this has some connitations that Kirt may or may not want. It depends now on what he wants the story to say. Grays in this would be clay-ish and Orange could be a rubbbery polycarbonate thing that light difusses through. Maybe Orange could have little round bumps, or maybe the texture of a raquetball (might be too subtle).
On the other hand all the characters could share the same base material but differ only in patern and color as the storyboards show. This gives them all a surface tie to one another without being too blatent about it.
Ok, done rambling, hopefully there is something of use in here. checks Oh, well 


