Andreas, do you have access to the wonderful Windsock Datafile Special "Sopwith Pup"?
Look at page 38 " PC10 Khaki (or, in some cases, PC12 Red-Brown dope)"
Another interesting read is the Windsock Datafile 22 "Sopwith Triplane"
There is an interesting discussion "PC12 on Triplanes" on page 31/32 ".. if PC10 stocks were low, PC12 were used."
I think, at least parts of this discussion was also valid for the Pup.
My two cents,
Frank