I'm still not so sure. We can assume that the Shared Stunt and the V2 at one point looked nearly identical to each other when they were both used as motorized dueling props in ANH and, more than likely, sported the same color scheme. But, at this point in RotJ, it very well could've lost that brass color (copper is more red-orange,
brass is the brown-yellow we see) on the neck/windvane as it used for filming. For all we know, it could be remnants of that brass that still remain when this shot was filmed but, grainy images just can't do it for me, now. Especially considering this image surfacing at SWCA.
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What that is on the windvane/neck of the V2, in that photo, for me can't be anything more than dirt on the hilt (these scenes were filmed after the Sail Barge sequence, if I recall) or artifacting caused by the digital scan of the film (and the saturating back and forth) that picked up the detail of the paint on the neck, having almost a two-tone effect, due to the handling of the prop over the years; tarnishing the original finish of the paint. There is a similar effect on my V2 when I photograph it because my paint scheme is in a similar fashion.
If you look at the "booster" section on my V2, you can see what I mean. It's the same black paint all over but the sheen has been dulled in sections from handling the prop. I believe this situation to be replicated in some form on the actual prop, and coupled with the photography of the thing in the film, then the digital scans and alterations made to enhance the image, that is supplying what some might interpret the coloring on the neck/windvane.
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