IMO, trying to find an accurate color for any railroad equipment is an exercise in futility. Especially for a car that existed over 70 years ago. There are so many factors which can affect the color. Starting with color photograph not providing accurate color info (due to fading, lighting conditions when it was taken, film type, etc.) Then there is paint fading and weathering (dirt).
Sure, you might be able to match some specific color chip from that period, but unless you are modeling fresh-out-of-paint-shop car, that color chip will not be accurate. And even if you use that color chip for reference, the RTR models will likely not match that color either. But I guess that would be acceptable, due to the factors I mentioned earlier. Variations are acceptable.