To answer your original question I believe they would have painted in Tuscan Red. not a box car red. They also painted engines in Brunswick Green and DGLE.
I worked with Dupont on trying to get the REAL color charts from there achieves when they supplied to "Dulux" to the PRR. The paint formula's have changed over the years as the Government outlawed paint types. I tried to recreate DGLE with Dupont who used there original formulas to recreate the same using today paints. You would be amazed on how hard it was to do. DGLE was supposed to have a touch of Green in it. I do have a shade of green on my Loco #9339 but it is really hard to see, even in bright sunlight. The Strasburg unit #9331 was done in Brunswick Green, not the right color but looks better. We are currently repainting it and will remain Brunswick Green. Our coaches are being transitioned to a Tuscan Red. We try to get close to the Drift cards as we can, but after a year they fad or get stained.