well this is a topic in it's self. First off most treads have rubber pads to contact the road, these should be painted a flat black. Next the treads themselves...these should be painted gun metal then dry brushed with silver or flat aluminum. (mainly the track ends) To simulate mud your going to need to talk to one of our more advanced and knowledgeable modelers.since i still need to learn this techniquee myself. Also on the drive sprocket..the teethe should be painted flat silver..since they are constant contact with the road and the tracks.
Hope this helped a little:)
~H~