Thanks, Mark.
The OD has some white added to fade or "scale effect" the look of it.
Also there is a pre-shade coat of Vallejo "field drab" underneath. I mottled this on over the white primer along with some straight OD.
The top coat of faded OD has about 50% Future mixed with it to make the pre-shade show through more. Also, the Future makes it very durable for handling and masking.
I was surprised to lose my rivet detail because Future and acrylics usually dry so tight that even some scratches show through. Perhaps I'm just putting all my coats on just a bit too heavy.
Airbrushing is really something that just takes tons of experience, doesn't it?
Oh well, it's not the end of the world that the rivet detail was lost.