I got a chance to briefly play with and watch @Loke demonstrate the concept hardware behind Windows Phone 7 Series at the Game Developers Congerence, and it seems that Microsoft is expecting more AMOLED displays and touchscreens. Windows Phone 7 engineers chose black and white backgrounds in the design element with AMOLED considerations–black backgrounds would save power by nature of how AMOLEDs work and the white background is used for emails and text to enhance readability.