Be sure to vary the weathering according to the location. For instance, in a station or locomotive depot with steam - in fact, anywhere where engines regularly come to a stand - almost everything, including the ballast, is black (except the rail head, of course) from the mixture of oil, coal dust and ash. The farther out you get, to the goods sidings and then the running lines, the lighter and rustier the weathering needs to be. If you are running close to the sea, then heavy, dark rust (from the salt spray) will be needed. In a late diesel or electric era layout, there will be lighter coloured weathering and rusting, but the greasy black lasted a very long time in yards where track was rarely relaid or reballasted. My branch line terminus is black or dark grey everywhere on the ground, and is just as I remember it, all but that heavenly bouquet of smoke and oil and creosote from the sleepers that could hang around a station yard for decades after the steam engines left.