I'm doing one at the moment of all nine characters - Mal, Zoe and Wash in gold, Kaylee, Jayne and River in red, which leaves blue for Simon, Inara and Book. I used logic where I could, but in the absence of any I went for what looked good. Plus, three of each balances out nicely.
Yeah, that works nicely. Zoe in gold makes sense--she's Mal's Number One, after all.
Can't wait to see the finished product.