While it could be tempting to weather the hell out of them, I selected a very subtle level of dirt and splatter to give them a realistic appearance while keeping them clean like the prototype.
It is too easy to overdo weathering on a light color car and I believe a light touch is often enough to give that "steel" look we want.
I also did the same thing with a set of Proto 2000 NSC newsprint boxcar in www.cn.ca scheme. I recall these cars used to be quite clean back in the early 2000s too. To be noted, I'm not in the mood of doing grafitti on my cars for obvious reasons: they weren't that frequent on Murray Bay Subdivision back then and I prefer to keep my rolling stock clean so I can use then for earlier years in the 1990s.