Again this is based on no theoretical knowledge (someone please jump in if you can help) but I guess the colours that fade or get shaved off from fading prints or through generational/pixel loss are those colours that are the finest or most subtle, the sort of extra sparkle/lushness/brilliance that pushes an image over the top into becoming incredibly 'right' and lifelike. For this kind of thing ideally as soon as film print is made it should be scanned with the highest possible pixel resolution / color handling. Even the technicolor dye print must have some tiny degree of loss in it (if negligible). My point being is that pushing the colours that are there around will at some point reach a ceiling in one direction e.g. the flesh tone can't get anymore flesh tone. I'm guessing a person could introduce colour back in digitally - you would be repainting into the film. The trouble is I don't think this could ever be done with the subtlety of natural light on film (well they didn't manage it with Jabba in Special Edition I know that for certain)
This is not meant to be discouraging feedback at all , just when you get into the finer stages of this correction I reckon its going to get tougher!!!
Have you seen the colours on this page:
http://originaltrilogy.com/forum/topic.cfm/Japanese-Special-Collection-Star-Wars-Trilogy-Take-2/topic/10521/page/2/
I know looking at loads of different sources can be confusing on the one hand but may narrow you in on the other. I guessing the last few corrections will have to done just by sense of what it would look a few steps on from one of the sources.
Its impressive what you have corrected in such a short time by the way and really shows up what little care was taken with the Gout release.
You could settle with what you've got so far but maybe you can dig out even more yet.
Hope you will post a clip also.