A freshly painted SP freight car looks significantly different than a car that is faded or dirty. The fresh paint to my eyes is a very rich, deep oxide red. But in less than a year that fades to something close to Scalecoat's box car red. If I am modeling a car that's going to be several years old I rarely use only one color. I find that applying slightly different shades -- prior to decals and weathering -- really helps to make the car look used. In general, I think the color that IMWX and Red Caboose applied to their SP box cars is very good for representing an SP paint job anywhere from 2 to 10 years old (after some added weathering of course).
