Regarding the livery of two foot passenger equipment. The cars had red roofs when new. The paint was called Red Lead. The name came from the use of pigment gotten from the acid that steel mills used to wash rust off of metal. The used red acid was sold to paint companies for the base color in the paint. Car builders Jackson & Sharp, Billmeyer & Small and Laconia all used red lead paint.
Some railroads had other liverys but generally passenger car bodies were painted in the Brunswick green that James mentioned. The color was common in the northeast prior to WW II. It is similar to a glossy dark Army green. We know that the SR&RL, B&SR and Maine Central used it. The original color of W&Q coach 3 was brunswick green with a red lead roof. As Mike said, soot darkened the roofs over the time.
