I've seen and designed a few sets with these designed into them. Notably, Mogoholic on her priest's page has made excellent use of the various color variations. If you haven't seen her website, Mogoholic, you should check it out! I had a lovely screenshot of all three, albeit my Death Knight was wearing the Arachnidian Robes. :p
There are 3 available coloration options of these spider robes, and accompanying pieces. The 4th coloration, was in the Naxxramas database back when it first came out., but the top half, the Watcher's Tunic, is available from a quest in Outlands. Let's spin this shroud of webs, shall we?