Off the top of my head I don't know waht color real M1 Abrams tracks look like or exactly how they are built.
What I did with an M3 Grant was to leave the tracks black, since the basic track blocks were actually rubber. I then washed with a brownish-tan, to simulate the dirt and sand from the North African desert. Lastly I drybrushed the edges and the guides with silver to simulate the metallic tread connectors. The effect was decent.
I used oil-based enamels for the washing and some difficulty with incompatiblity with the rubber tracks. I have heard that acrylic paints work better in that respect, but I have never tried them myself.