I don't know if this will help shed further light on this subject, but here goes. I have a 2007 XLR-V, Xenon Blue (color code 19U). I bought the vehicle from the U.S., used, and with the paperwork was what I believe to be a photocopy of the original factory-to-dealer invoice. Although it does not show a GM letterhead, I believe it to be a photocopy of the original invoice because it gives not only the "list" price (M.S.R.P.) but as well the price actually charged to the dealer. My car has the cashmere interior, with ebony (black) trim around the tops of the door panels, on the roll hoops, and on the fold/flip-up covers immediately behind the seats. This color is referred to as "Cashmere With Ebony Accents" on the invoice, and the color code is shown as 313. Incidentally, my understanding is that through 2006, the light color interior was called "Shale" which is a noticably "whiter" color than the light tan color cashmere.
Hope this helps.