color for the tracks

Well, my way of doing things is the following:

Paint the whole track in a dark red-brown colour (mix red and black if need be), then let dry. I usually use enamed for this. Then use a 'wash' of black or sepia all over again. A wash is a very thin mix of a colour and a solvent. For this stage, I use water-based colours in tube - like the ones artists would use on their paintings -. My wash consists of some black (or some sepia), some water to which I add a drop or two of white vinegar and a drop of whasing up liquid. The washing up liquid helps breaking the surface-tension of the water-based mix and it can fill all recesses. The vinegar helps reducing the watermark effect once the mix has dried out on your model...

If you use a wash with an acrylic paint, use denatured alcohol as a solvent. A drop of washing up liquid will help too. If you use enamel paints in your wash, use white-spirit as a solvent BUT make sure the red-brown of the tracks is VERY dry, if not that solvent will attack the base colour.

With water-based washes, I use a hair dried to speed up the drying time. You should then see a darker red brown base colour and the darker shade of the wash left in all recessed, giving definition to the tracks.

Next stage is highlighting, using the dry-brushing technique. Use a flat, rather soft brush, and a lighter shade of the red-brown colour to highlight the tracks. With little paint left on the paint brush, brush the tracks and the paint will deposit itself onto all raised parts of the tracks, adding to the definition of the tracks.

Then drybrush, VERY lightly, with a bit of silver paint. Do not forget to put some silver on the teeth of the drive sprocket!

Your tracks are done. Now they can be, if required, weathered with dust, mud,... to fit your base/diorama.

There was an article a few months ago in FSM, and the author proceeded pretty much as djmodels1999 says, except that he used a blue-black base color, and finished with a steel drybrushing. Tanks in cold, wet climates like Europe will have some rust on the tracks, as well as mud, ice and whatever else the track has been in contact with. If the tank has moved much recently, the ground surface will tend to grind the rust from the areas of ground contact. The Germans, Russians and British used all-metal track on their native designs, but Lend/leased US equipment mostly had rubber track shoes. Tanks in desert areas, which would include southern Russia and the Ukraine in the summer, would not have so much rust on the tracks.