Doh! Now I get it. Two different sides, and, yes, I've seen that on any number of freight cars over the years.
I'll scan that pic in later today, and one of your sixty footer as well. I might even throw up a couple or three more in a separate post, as I've wondered (since I first saw your cars) just how YOU might handle a certain rust situation.
Nothing needs adjusting where the trucks and wheels are concerned, IMO. I would be hard pressed to say "this is right" or "that is wrong" where freight equipment is concerned--one photo can differ so much from the next I really don't think it can be pinned down in any real way.
The D&RGW's "go to" ballast--at least in Colorado--was a dark grey, almost black slag. It was sourced from Malta, near Leadville, and perhaps from Pueblo too, where Colorado Fuel and Iron is located. Thus the track and ballast look quite dark, almost as though you took a wood-burning iron to the scenery. I would hazard a guess, then, that the underframes/trucks/wheels would tend strongly toward the dark side for that reason alone.
D&RGW motive power, on the other hand, shows the opposite: Though the black locomotive "superstructures" are mostly different shades of grey after six months, the undertray is decidedly lighter--sanded rails do that, and the Rio Grande needed a lot of sand.
As with SP/Cotton Belt, things are generally grimy too, and it happens pretty quickly unless the equipment is washed. Moffat Tunnel (Rio Grande), and the Donner pass snowsheds (SP/Cotton Belt, where trains can linger a long time in the level-fall sheds, like the one at Norden) make things dirtier quicker than with many other roads--UP comes to mind, where everything always seems cleaner.
The grime was generally removed on passenger equipment (spray washed in Grand Junction twice a week or more I think), but I don't think other motive power went anywhere near the wash track. Kinda like the way some kids can be so adverse to taking a bath.
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As far as taking breaks: Mario Andretti was interviewed on one occasion about what it takes to be a consistently fast race driver. "Practice...a lot. And if you plan to do this for a living, take very short vacations."
[Paraphrasing mine]