About your comment or question regarding colors. I may not have read it right but here we go.
My best info is that the color of all underside structure was painted black. A lot of the chassis construction was iron and black was the color of choice for preservative.
It appears that all European railroads used a “boxcar red”, the common iron oxide preservative. There were dozens of variations in the US - some circumstantial due to pigments and carriers - some intentionally mixed “just to be different” and based on what an engineering department’s staff decided was a better mixture.
I don’t know what is recommended for the exterior color of the German rolling stock but Armor 35, who cooperated with the Pereslava Railway Museum in creating some of their models, listed MiG Red 0.49 as the exterior color for their Ua boxcar.
As a reformed but still active rivet counter, almost any reddish brown should suffice. Weather, age, consciousness of the painters in the car shop, all affects what color you will see. Original color US movie film after the war of POWs on a train showed a crazy quilt of colors. Some more or less uniform, some showing signs of recent painting from RIP. The only thing I don’t recall seeing was bare wood.