I know one thing that I remember distinctly is that Hoth was always an icey blue. Definitely not the straight snowy white that Lucas has changed it to in the more recent home video versions. So the cool icey blue of the snow fields and mountains is correct. The trick will be getting the precise color as close as possible.
As to this 35mm print, it's great to hear of a print in such fine condition. :) I wonder how it compares to the prints of those who will be continuing on with negative1's 35mm restoration after Star Wars is done. Makes you wonder if this one might be an even better one to base the restoration on than the 35mm prints they are going to be lining up for The Empire Strikes Back. And if he might be willing to let them have access just long enough to do a HD scan for the restoration. Then he would have a superb quality back up of his print on Blu-ray. =)
In any case, I hope at the least that very high quality photos can be taken during a screening (with the projector paused for a few seconds on various scenes to give a good sampling throughout the movie) with a nice SLR camera on a tripod, with the white balance, exposure and such set correctly manually to get the most accurate shots of the movie possible. No doubt the camera/movie experts on the forum here could advise on the best camera settings, lens types, etc. to take photos with.
This could be a superb reference for color restoration for Harmy and everyone else working on such projects. But whatever you do, please don't compress the images, so as to leave the colors fully intact and unaltered. Have the camera take them and store them as uncompressed bmp's, tiff's or whatever. I guess it would be in 32 bit color, or maybe even 36 bit (the next step up in color detail/gamut, IIRC) if the camera supports it (not sure if any do). I hope all goes well with this. :)