The bluray certainly is the worst color reference to use, as it was heavily altered when it was digitally color graded to fit GL’s vision. There literally is nothing authentic in the bluray color grading, as it was scanned directly from the negative and completely regraded. The GOUT, just like any of the laserdisc masters was also regraded, where the brightness and contrast were adjusted on a scene by scene basis to fit the low contrast medium they were made for, so they do not correctly represent the variation in the grading between scenes. Take the JSC, where the R2 canyon scene was noticably brighter than on any print scans we’ve seen. The Technicolor print scans are definitely the most accurate source for both the colors and luminosity, despite the problems of green shifts and other issues that we know of.
The magenta and green blotches in the Tarkin frame are artifacts that are being corrected as I’m writing this. Many of the Tatooine are preliminary. The only gradings the are close to finished are on the first page.
Well, I agree that that the Technicolor print scan would be the most accurate provided I had a copy and it was a raw scan and the same settings were used for each reel. At present that is not something that is publicly available. Of the sources I have access to, I found the GOUT/Definitive Edition to be the most accurate. With the exception of the opening shot. I have become convinced that was scanned for the first DVD set special feature and edited on for the 2006 DVD release making it a higher generation than the rest (and it looks like it too). And I think you give them too much credit for adjusting scenes. I don’t think they put that much effort into it. I think the entire movie is supposed to be darker and I feel that TN1 SS edition really proves that.
Now, in the four examples you posted above, I find that R2 looks best in both the GOUT and JSC versions. I’m not sure how many R2’s there were or if they featured different paint jobs, but all the Tatooine outdoor shots feature a very bright blue R2 and all of the indoor set shots feature a very dark blue R2. I’ve found R2 to be a good guide as to how accurate the behind the scenes photos are and a great many of them are way off. If he is green, purple, or nearly black, the photo isn’t accurate. If he is bright blue or dark cobalt blue they are in the accurate range. C-3PO is also a good guide, but not as good. If he is too orange or too silver the image isn’t good. He should be a nice yellow gold just slightly to the brassy side instead of the elemental gold. But R2 is much more reliable such as in this behind the scenes photo - http://www.moviestillsdb.com/movies/star-wars-i76759/JcR6OH