The screen is comprised of three layers. The bottom layer reflects ambient light back through the top two layers which process it into a colour image. Like electronic paper once the pixels have been ‘written’ almost no power is needed to retain them.
Japan Display Inc. says that they’re ready to ship the version with a lower colour range, but the high colour gamut version still has some issues. Even so, both versions look perfectly usable. Who knows, maybe in a few years our mobile phones will have battery lives of weeks instead of hours.