Sure, where such things are possible, nothing beats a color separation master or a reference print, and that certainly works best. But these things simply aren’t possible with our Star Wars preservations, so I didn’t think that was particularly worth getting into. The best we have is low-fade prints, in the form of low-fade poly, late seventies dye transfer, and in the case of ROTJ, the simply better filmstock of the era (and some lucky showprint finds). Because they’re not perfect color references, they can serve only as starting points, so the question is how do you know where to take the color from there? After all, if you have several prints on the same fadey media all struck from the same master, thirty years later, they will all look different due to differences in storage conditions if nothing else. How do you know how they looked thirty years ago?
DrDre actually has multiple tools at his disposal. One is his famous color matching tool, which as you correctly point out doesn’t have a lot of value here on its own. But another is his color correction tool, which is where the value is (discussion thread about both tools – I see the confusion now, he’s renamed the tools multiple times so it’s hard to keep them straight). Using color theory, the correction tool (or whatever he calls it these days) estimates the original colors of a single faded image (selected for how well it represents color primaries). Then, using the CLUT created from that single frame, you can use the color matching tool to restore the rest of the shot. You then have something very close to where that print actually started before fading.
And yes, it’s not 100% objective science, there is a little art to this as well. Dre does apply small tweaks to his corrections after the fact. Sometimes there might not be a frame within a shot suitable for his color correction tool, so you’d have to estimate. I suspect he also likely adjusts contrast and black levels to match modern audience expectations, for example, or changes things for consistency. But this tool is key to why his colors are generally closer to objectively correct, in my opinion, than most.