The good looking color stills could have been single-frame color correction tests, not excerpts from color-corrected footage. They may have been corrected in Photoshop just to see how much color info could be extracted from the image in the actual transfer. That's a much more plausible scenario than "hoax".

If it were a hoax, explain the Cloud City scene that was just posted. I've been following this from the start, I was on the old private blog, I saw the behind-the-scenes footage (including monitor playback of footage from the final reels, with the same color fidelity as those stills), and this is definitely legit.