Tracks and track shoes are a real conversation starter. Yes, the Stuart track you're modeling had rubber shoes or pads (called blocks in WWII). The end connectors (WWII... Links) were steel. Anyhoo. A track will pick up a lot of dirt even on pavement and start varying away from a pure black (Unless skidding around a turn). A clean track shoe will be anything from dark gray (clean) to brown or tan to light sand depending on what the tank is running through. Once on a harder surface, pavement or even harder ground, grass, this 'mud' tends to wear off quickly, with the color only around the edges. So, you can paint the tracks black, wash the tracks with a lighter color and then wipe off the bottom of the shoes where it contacts the ground to give it depth.
The links (WWII), or end connectors (now), will be shorn of rust in a fairly short time and will become steel colored with sand, mud or what ever stuck to them. So, a base of (dirt, sand, mud) color with steel highlights looks nice.
This past weekend, we ran Paladins through wet sand. The shoes became steel colored with sand in the nooks and crannies, while the pads were gray black with lighter gray side areas. Where the track guides meet the road (bogie) wheels, they were rubbed to a high shine, as was the wear plate on the wheel.
The track on an opperating tank is seldom rusty, unless the vehicle has been sitting for a long time.. then it tends to be light (orange) rust. The mud and grime really add character to an otherwise dull steel track.... on a running tank, that is.
Sorry, didn't want to write an article... next time 'live' vs. 'dead' track.
You have a lot of latitude with tracks, so have fun!