I’m about to start weathering my Sherman (WWII). What was the primer coat color? Would I be safe just using burnt umber for the “scratches” through to the primer coat?
Red lead oxide primer is your color. The general consensus seems to be that US OD paint is extremely durable, and while scratches do occur, the current craze of paint chipping tends to be a bit overdone, especially on OD, so go easy on the chips and scratches.