Did some more googling. Most sites – including Tae Kim and Wikipedia – don’t mention の-adjectives at all. Of the sites that do, pretty much all of them admit that they’re just nouns. One site mentions they’re functionally the same as な-adjectives (which are often call adjectival nouns anyway) except that they use の instead of な – it also uses the example of みどり, which I’ve always been taught is a noun.
My textbook doesn’t discuss them in any detail – it is, after all, an upper-intermediate-to-lower-advanced-level textbook, so that sort of grammar is probably assumed.
Soo… I’ma stick with my first comment: they’re just nouns. =)
はやく!みどりじゃないワイアを切れ!