Ah… searching for more pics led to this - http://cdn.moviestillsdb.com/sm/ba5c5aacb00c284692aa349bb8006836/star-wars.jpg
I’d say this is an ideal image for the Tatooine desert/R2-D2/C-3PO colors and the skin tones (though they are hard to see they are reddish and consistent with the blistering temps in Tunesia).
The problem is that the Tatooine desert has a different color depending on location, time of day, and weather conditions, and can range from more yellow, more red and brown. I’ve watched hundreds of production photos, and there’s something unique in all of them.
Ah, well when just looking at the natural color of the desert, don’t forget to check out all the more recent tourist photos of the old locations as well as Episode II (and those production photos). While I too have noticed some variation, the photos that have that distinct yellow tint do not look very natural and the other elements (such as R2) aren’t the right color in a lot of them. They also tend to have washed out or jaundiced skin tones. You need some red to the skin tones, just not as much as the DVD and Blu-ray have.
From what I’ve seen, that yellow color seems to be indicative of the 1977 production stills and can be found in more than just the desert scenes (like the Death Star, Blockade Runner, Cantina) and does not appear in the more modern photos taken in Tunesia. I don’t think that yellow color is reliable or accurate.