I recently read an article that seems to be relevant to anyone painting RFC aircraft. PC10 was a powder, apparently a mix of 250parts yellow ochre to 1 part lamp black by dry pigment weight. As Yellow ochre is based on iron oxide and is very heavy this is not so uneven as it seems. The resulting brown powder is mixed into the finishing medium, either cellulose acetate or oil based varnish. In either case the medium caused the finish to look slightly green when new, fading to brown as the aircraft aged. Oil finishes were used on ply and metal and looked more green than the cellulose applied to fabric. The base colour of the powder could also vary depending on the source of the yellow ochre which could vary from yellow to orange. Looking at the aircraft in Old Warden and Duxford I would say that the Tamiya Khaki Drab is about right but the greenish tint will be difficult to make. Finally, if the article is correct British aircraft were glossy when new. Extracted from an article by Kenneth Munson.