I think that the color you ask about was called P.C. 10 (Protective
Coating). There was a specific formula involving lamp black (charcoal)
and a yellow pigment (?perhaps another ingredient?) which together in a
carrier dope produced a color
that has variously been called khaki, chocolate brown and brown-green.
There was a second color P.C. 12 that had a decidedly more brown color to
it, however, I have no idea what it was made from.
I seem to remember a couple of the early Windsock issues, back when
he included color chips in each issue, had samples of these colors.
However finding copies of these would be pretty difficult now.
Charles Hart
hartc@spot.colorado.edu