Hello RAGIII
Reading your post reminded me of something I'd read - it's from "Fighters 1914-1919" by Kenneth Munson and at risk of copyright infringement I quote part of the chapter talking about PC10:
“it’s natural pigments were natural oxide of iron(yellow ochre) and lamp-black (or carbon black).. They were first mixed in a ratio of 25 parts yellow ochre to 2 parts lamp-black by weight of dry pigment-not such an unbalanced mixture as it sounds, since the yellow ochre weighed fairly heavily while the lamp-black was extremely light in weight. When mixed together these can only result in a darkish-brown shade. What has given rise to the “green†part of the description is that, for protective purposes, this dry mixture was intermixed with cellulose or oil varnish or some other glossy liquid medium, when a curious effect known as “green shift†takes place, giving the finished coat a tendency to look slightly greenish under certain lighting conditionsâ€
Regards
Chris