You did understand what I was trying to convey, even though I knew at the time that it was awkward sentence structure. MP followed a practice that a lot of railroads did at the time, that open-top stuff and locomotives were black and roofed equipment was red. So in the early fifties as you're concerned with, the plows would naturally have been black. Surely there's a photo out there showing one, but much less likely that a painting drawing still exists. No doubt, though, that those photos are probably B&W. So I agree the question of the plow surface is still open, but I'm willing to bet that it was aluminum. Charlie was a lot more in contact with the MoPac than I in that era, since I was just a bystander. and he's a second generation MoPac.
MoPac did use a lot of aluminum paint in that era for certain things, for instance black and aluminum candy-cane striping on grade crossing signs, and locomotive lettering had been aluminum leaf.
The orange color used in the sixties was probably ART orange, which some shops might have had on hand. It's clearly different from the yellow that was used in the sixties on the ends of occupied house cars.
Occupied house cars (ex-boxcars and ex-passenger cars) and maybe some other stuff, were either boxcar red (mostly) or light gray. In the early fifties I think they were all one color, in other words they didn't have yellow ends or anything. Anything that was mostly steel, like cranes and flatcars and so forth, was black.
Model notes: that Hallmark model isn't put together very well, so when I rebuilt it in the 90s I may have put a cut-up Athearn frame under it, or parts of one. I'm pretty sure the trucks under it are Lindberg because those were the lightest ones that existed at the time. The prototypes probably mostly had 40-ton trucks, or whatever was available at the time. I carved most of the journal box off the front truck's front axle for clearance. I'm sure it still has a Kadee 5 on the back end.