This was a question that came up on Twitter during the night. Since I’ve done some Windows Phone development and I understand that WP developers might want to do this in WinRT apps. Unfortunately this cant be done. At the moment you cant access the screen background color for usage in the application. The sandboxing prevents us from accessing system settings, which I think is understandable.
If this changes, or I’m wrong on this one,- please let me know. Seems to be a popular question!
A few links: