Microsoft thinks AMOLEDs are the way to go

Folks at Microsoft – their engineers, specifically, have been reported to pick black backgrounds in Windows Phone 7 simply because it will come in handy when working with AMOLED displays – after all, AMOLEDs and OLEDs do not consume any juice where black pixels are concerned. Apart from that, folks who want to do plenty of reading can check out the white background option as it supposedly enhances readability.