for what it's worth, here are the tracks i've made for a project i'm working on. I'm at the stage of drybrushing the metal parts that are exposed due to friction;
i started with a light rust colour and applied several tones of pigments, dark rust, light rust, dark earth, light earth. I have fixed the first layer of pigments with terpentine, the second with white spirit, and the last two are just powdered without any binding solution.
the last step will be a lighter dusting using the same pigments on the tank and the tracks, but i'm waiting for that until i've finished the base of the diorama it will be placed in, to get a nice cohesion of the colours used on both the ground and the tank.
first picture shows a painted track and a track with the first pigments applied to it
after applying the light rust (top one of the two tracks shown each time) and dark earth (bottom one) this is the result:
after the light earth pigments this is the final result:
all that needs to be done is use some silvery paint and a simple crayon to simulate rubbed metal.
hope you liked it.