Factory and shiny metal (steel) color, then wet, muddy, snowy area and oxygen (air) benefits after rusty.
However, where the track meets with other substances, there metal polished.
In such places: the track grip nails, line rollers, chain-wheel-drive track meets, baffle plates (combs, tooth).
Perhaps the earthy, muddy soil in some places it may stick in the winter, the snowy parts of the vehicle while it is moving, and the desert entirely glossy csiszolódik and then, once rust starts.
Today's chain of bases involved, heat treated, surface treated.
They are also colored brown or blackish.
In use, it can wear, where wear, rust as well.