The screen is a transparent window, since these are transparent LCDs.
However, in IFR conditions, when all you see outside is white or black or grey for that matter, the LCD 'window' will be switched on, and it will display:
What you describe is basically an augmented reality system. Those are in development right now and are usually based on glasses, not on covering all windows with transparent screens. Check out
· Aero Glass for example although that is build for GA and based on traditional EFIS symbology.