Not in the B7 A4, but for a sense of color check out the gallery of Audi's from the Geneva 2004 auto show. They had several cars in Quartz Grey Metallic. I tried to order it for a B6 S4 but of course it wasn't available so ordered Avus silver instead. There's a link to the galler on this site somewhere.

Quartz Grey is really nice. I would order that if I were in the market for a B7.