This from the principle/premier Customization website? Sounds pretty odd.
I think it's an issue of usability Doc, for some people it might be to hard for them to see, and being that they are buying it, if they end up with something they can't use......it will just cause too many problems. The Skinner can include substyles, but they must have the white.
Tim, instead of having to do a substyle, couldn't You just include a TGA swatch of the color You wanted it to be? people could just drop it in C:\Users\Public\Documents\Stardock\WindowBlinds\Textures........ then they could select it from Explorer Backgrounds in WindowBlinds just like You would for a texture. Of course this may cause some usability issues depending on the text color, but if You can find a color that looks good with the blind and use a font color that works well with it and the white........just another one of those ideas that pop into My head..... 
