Well, here's something interesting. According to tipster Josh S, a perusal through the Zune Software source files will net you pictures of four as of yet unknown Zune HD palettes. From left to right, we've got pink, magenta, purple, and "atomic." We're still looking through the source code ourselves to confirm. It's not like early adopters wanted anything other than platinum and black anyway, right?
Update: We've finally come up from digging through source code and, sure enough, those images are all in there.