I'm working on my helmet here and I'm using a custom mix that is nearly, if not spot-on, accurate to the movie helmet. In the same ballpark as Lee's (rogue studios) color.
I needed to touch it up but couldn't spray for such a small fix.
I used regular $.99 2oz acrylic paints that I had lying around, hoping I could get it close.
Apple Barrel Plaid's 'English Ivy Green' "20756"
DecoArt Americana's 'Graphite'
I don't know the exact mix but it was like 2/3 green and 1/3 graphite. It's probably more precise than that, but that's the basic idea. My mix was very close and I'm sure that with some tinkering it could be exact.
I know some of you are stuck handpainting your helmets, thought this might help you out