Remember too that the clerestory sides normally had windows in it, it was designed in pre-electric light days as a way to allow light into the car beyond what was available thru the side windows. They'd want to be careful not to get tar or whatever on the windows.
The turn-of-the-(last)-century standard roof was tarred canvas, hot tar applied after the canvas was in place. After a liberal coating of fly ash it would weather out to about the same shade as an elderly asphalt road.
The vertical sides of the clerestory would have originally been painted to match the car sides, but might have gotten tarred during roof maintenance.
Chuck (Modeling Central Japan in September, 1964)
From what I've learned, it wouldn't be unusual for the sides of the clerestory (where the windows are) to be the same color as the body. Generally the roofs were black on passenger cars and cabooses. I'm not sure if they were painted black or if it was a coating of some kind "painted" over the canvas material, like creosote or tar. (Maybe something more like tarpaper was applied??) If so, it could be the pic you're looking at was taken before this final step was done.
Canvas was the chosen material, I suppose it could have had some finish applied that no doubt required frequent refreshing due to soot and cinders, on the other hand, it could simply be varnished and what you are observing is the result of the fabric darkening upon drying.
Dave
I'm painting some LaBelle 1906 era wooden passenger cars. Most commercial models of wood and steel clerestory roofed passenger cars seem to come with all black roofs. I expect this may be correct for steel cars when there were no windows on the vertical sides of the roof, and probably also on later repaints to save costs. But what about when new? In Dubin's "Some Classic Trains" the majority of the individual car photos are builder's photos which seem to show the vertical side of the clerestory in the same shade as the sides of the car body, as does the full color Pullman foldout in the back of the book. But these photos also seem to show a much lighter color on the roof. Were the roofs a light gray? Did the builders just put a temporary color on the roof to enhance the photo like locomotive builders did? Is it just the way the matt surface of the canvas covering reflected the light (but if so why is the shade so consistent over the curved surfaces)? Are the photos all retouched? Thanks.