Looks like primer spots, maybe on it's way to a repaint? or the scrap yard?
Thought it was interesting.
Mike.
My You Tube
Yeah, Mike. That's one of those "real-life" things that if you modeled it, even with 100% accuracy, it would look awful on your layout.
Kind of like the paint job on this mill building here:
Weirton_mill by Edmund, on Flickr
I agree with your assessment that that is filler putty and, for whatever reason, the cabbage is in transit or got pressed back into service. Or Amtrak's paint budget got cut (Imron is very expensive!)
Cheers, Ed