Well, they may have faded, but those cels will have the final color correction baked in - it's just the way they did it then. The only print that wouldn't have any color correction applied would be the first interpositive, and maybe an internegative after that. (If what I understand about the pre-digital color timing process is accurate.)
My only thought is whether or not the 70mm version had different color timing than the 35mm version.
Now, you may ask, "Wouldn't they make the 70mm blowup from the color-corrected print?" Not necessarily. That would mean using an answer print struck from an internegative struck from an interpositive (that was possibly also struck from another internegative, which was struck from yet another interpositive) that was struck from the camera negatives.
This, naturally, means all the generational loss of a 35mm release print, just blown up to 70mm. But everything I've heard about the 70mm print says it has to have looked better than that.
So I think it's more likely that the 70mm blow-up was made from either the camera negatives (less likely), or the first master interpositive made from the conformed camera negatives (more likely). That would mean it would have to go through the same color timing process, but in 70mm (resulting in much less generational loss, though the release print would still be a copy of a copy of a copy of a copy).
Then again, that may have been too expensive, so I could be wrong and the 70mm blow-ups could have been struck directly from the final 35mm answer print.
I do think that Empire went through two distinctly different post processes for 70mm (first) and 35mm (second), accounting for the slight differences in editing, effects, and sound. So the 70mm Empire probably did have distinctly different color timing than the 35mm.
I have no idea about Jedi, though (seems to be a common theme for that film).