Steve,
I looked through the photos I have and don't any color shot of any of the pre-war cars in their as-delivered color with reliable service herald. FWIW, the paint looks on the dark side, I tend to believe the Red Caboose model has correct color on it. The only color photo I have seen of an earlier car is a war era shot of a CNW yard from 1943 including a single sheathed Monon 2000 series car, see attached for a snip. It looks to me more like the brown the Southern used. Also notice the black roof. BTW, Mont Switzer has recommended using oxide red mixed 50/50 with boxcar red to get the post-war Monon color.
Regards,
Mike Aufderheide