@3rail (Donald) - I was expecting a lot more response to this topic. I have seen the "Camo" colors you mention. They are almost always available at Wal-Mart. I really like the Rust-Oleum textured spray paints. My favorite is the Aged Iron for pavement and Desert Bisque for things such as concrete piers, etc.... However, the texture size is only good for O scale. I'd like a finer texture for HO scale.
I'd have to put some covering over the rails. With my aim, I'd get more on the rails than the ties.
As for concrete ties, a different ballast is used. I'm not sure what the appropriate modeling medium would be. It looks almost like sand from a distance but I suspect it's some mixture of materials.
FYI: I never spray paint indoors.
Anthony