Look like I'm a little late to the party, but I wanted to get a better look in the chasm of the Valley Forge
so o messed with the levels a bit. Here you go, in case you wanted to see too.
Also, as to R2-D2 having black panels, it's the same reason as why the Imperial officers sometimes have black rank insignia instead of blue: the blue color gets chemically stripped from the film stock when they used blue screen to optically composite images. In fact, that's why blue is the color for bluescreen; blue was the top layer of film color, so most easily removed, also, there is very little blue in a human face, so it's the easiest color to work around. But little blue panels like on R2 and those rank pips, become transparent on that film layer and the black space background shows through. If you read George Lucas's novel of Star Wars
you may notice that Luke's X-Wing was originally supposed to be Blue 5 rather than Red 5. But the compositing process using bluescreen would have not worked with blue striping on the model, so they changed it to Red.
I imagine this is why the Excelsior
was photographed to appear as gray as possible also, for fear of the blue parts turning transparent (and therefore black) in the final print.