I am currently working on a user control that has white text and a transparent background. Unfortunately because the XAML design view within VS2010 has a white background I cann
Alternatively, as of VS 2013, you can do this in Tools -> Options -> Fonts and Colors, XAML UI Designer.
The editable foreground / background colors there are the colors of the checkerboard background. I just set them both to a darkish grey color that seems to work for both light and dark theme'd background stuff.