These are "reflective" LCD displays, where there is a one-way mirror between the LCD and backlight. In daylight, the backlight is actually off and the display is illuminated by the light around you. Pretty common e.g. on all sorts of boating displays (GPS/Radar/Sonar/etc.).
And it's a shame that nobody makes an Android device for the long tail of special interest use cases where a transflective display showing some simple custom app would save the day.
