I have always been under the impression that R2 had a two tone paint scheme, in that he had 2 different colors of blue that alternated. I figured this was a similar technique to the two tone paint scheme on vader's helmet to cut down on glare and to help define detail on camera. But with all the accuracy nuts, I have never seen a fan built R2 that featured this paint job. It's most noticeable on the closeups on ANH in the tatooine desert scenes. I'll get a screen grab.