My technique is pretty simple to paint tracks, no matter what the medium (plastic, metal or resin), workable or not. Color selection is pretty easy: pick out 4-5 red-brown and orange shades of varying darkness. Put the darkest aside for last. First, I start with a thorough overspray of flat black from a spray can. I use the cheap stuff from Home Depot and make sure everything is covered (see 1st picture).
Next, I start with the second darkest color and airbrush a zigzag pattern across the face of the track (see 2nd picture).
Third, I take the lightest shade and turning the tracks around I repeat the zigzags. Then, I go back to the third darkest shade (see 3rd picture).
I finish the zigzag patterns with the remaining shade (see 4th picture).
Whether they overlap or not isn't particularly crucial; it needs to be random. The last airbrushed layer is the darkest shade and I thin that out well before misting it over the entire track (see 5th picture) in order to blend the colors together better. I let that dry for about 30 minutes and then turn the tracks over and repeat.
My last step is to do some dry-brushing of the raised portions of the tracks with some steel-colored paint (see 6th picture). Being that this is for a World War One vehicle and you do not see the inside of the track, I did not do any dry-brushing. From there, you can proceed with your favorite earth/mud/dust techniques to finish the effect off.