Big Jim,
Exactly what color is it then? (Which seems to be the second most important question in this thread next to the one that comes with the title.)
Mike
A lot depends on the era one is attempting to model. If you are attempting to duplicate the 1930s thru 1950s "steam era", then the mainline rails would have a noticeable greenish hue, due to the color of all the oil lubricated plain bearing equipped freight cars. That oil was Texaco HD57 "JournelTex", and was noticebly green. All that greenish journel oil tended to coat the sides of the rails over time.
Now, if you are attempting to model the more modern era, the side of the rails tend to be sort of a dull gray/brown, since there is no more oil from the car journal bearings. Also, in the modern era, the brake shoes are all composition, i.e. no more cast-iron brake shoe dust that turns rusty color.