I recently "ballasted" my almost 3x30 foot yard using Woodland Scenics Fine Ballast Gray Blend # B1393. I applied it over the rubber anti-fatigue mat I'm using for roadbed by sprinkling it on top of gray paint.
It looked too light for me when I was done, but when I Googled "Typical Railroad Yards" the photos I looked at looked just as light as what I have done:
To me, darker looks too dark at our scale. I may dry brush some black on top of the ballast or spray some Rust-O-Leum American Accents Stone Textured Finish Stone Gray Stone paint sparingly to give it some contrast. As of now nothing will be put between the rails, but that may change. I used 1-1/2 shaker bottles of the Woodland Scenics stuff, went a long way.
I do need to sprinkle some cinder material around the coal tower.
here's an earlier shot of another place on the layout using the Rust-O-Leum spray paint:
Just after painting the sides of the roadbed, still has masking tape covering the rails:
