TTX flats in general see pretty heavy weathering - not rust, but road grime and dust to the extreme from a combination of speed and air turbulence around the vans.
I've studied "Super C" photos by the hour and half the time you can't identify the cars or the trailers without just the right angle. It's a dusty, and grimy, blur. Same thing with most roads that ran any kind of expedited TOFC service above 50mph.
It's entirely possible that you couldn't tell yellow from brown unless you've got a closeup shot.
It's fun to have one or two 'clean' cars or trailers in a train like that though.