shoemakesmusic,
The military controls use custom bitmaps for the background so you cannot programmatically change the color the way you can with un-customized control.
I haven't tried it but off the top of my head it seems like the easiest way to get the functionality you need would be to make the slider background transparent (using the recolor tool) and carefully place it over the top of a picture ring. In the picture ring you would need to have a bitmap with each color variation you want to be able to change to (the original source graphics are available to download from the same page you got the military controls). You would then change the picture ring to change the background color.
~SimonH