Christ-Guard,
I think (or thought) the newest version offered the option of a gradient along the path.
With that you should be able to create and use a gradient as follows using four stops (the squares under the Gradient Slider):
1) Set two stops with the starting colour at 0% and at 50% (or wherever you want the change),
2) Set two stops with the ending colour at 50% (or wherever, right on top of the other) and at 100%.
Without that, you can simply create the Art Brush from two horizontal(ly) abutted rectangles.
