So I have a few thoughts I’d like to share about the paint work on the armor itself. Please feel free to correct me if I’m wrong, but this may at least be a good start.
I was told not too long ago that there was a discussion that took place that ruled in favor of the fact that in Rogue One, Montana Gold Professional spray paint was used to paint Shoretrooper armor. I have no idea if that's accurate or not, but if it is in fact true, I really do believe that the weathered armor pieces (not the helmet or metallic armor) was probably painted with that same brand, and then weathered. I haven't done too much research on anything other than what I think the brown might be, but as for now, I personally believe that the brown is most likely to be the "Orange Brown" that has been weathered (The orange brown is the top spray can on the attached image).
My idea is that what they probably did was spray the whole piece with orange brown, detail the silver scuffs with a brush or airbrush, or you name it, potentially sealed it off (don't ask me what they sealed the Montana Gold with, I'm not even sure if you can seal that stuff, I've never used it), and then began the more intense weathering with different levels of black and a "sand" color. Then the scuffs showing the bottom layer of the more "orange brown" color could be done by physically scuffing it gently with a sanding sponge or some extremely high grit sand paper.
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