Try looking at the various paints used for "weathering" art and or garden items such as urns, pots and other decor. I noticed this stuff at the local hardware store and was surprised. They have multi part rust and patina paints, simulated wood grain paints, aged iron paints, stone-marble-granite paints, vinyl and leather look paints, etc.
The color you have on your tracks will probably look even better once you run it around in the dirt a little.