If you don't count the 1995 Botcon exclusive Nightracer repaint, the next most valuable colorations of the first 6 spychangers molds has to be the Jusco exclusive spychangers. Originally given away as a promotion at the Japanese retailer Jusco, these toys were blind packed. So you didn't know what you were getting and you had to get them in the promotional window. Therefore assembling a set of these is nigh impossible. I was lucky enough to get these from an ebay seller from whom I had purchased legitimate Jusco exclusive Wrecker Hook and Indy Heat. Although according to tfu.info Jusco is a misnomer for one of that pair as Wrecker Hook was technically to quote the site " Availability: This figure was available exclsuvely in Daiei stores in Japan in 2000 with the purchase of Build King (2000, Japan)."
Anyways the Jusco spychangers have a nice set of photos over at ridforever.com. Here is the only picture of the collection I took before selling it off at the right price.