Google was granted a new patent (filed in July 2013) that describes a technique for saving power on mobile devices with OLED displays. Basically the idea is that the when battery is low, the system can change the display characteristics (lower the resolution, disable animation and use red and black colors only). You can see the basic schema from the chart below, which is actually quite badly written: there's no option for a normal mode, and there's just one check and no loop as there should have been. Oh well...

This patent is only useful and valid for OLED displays. I'm not sure how canceling blur and animation actually conserve power on OLEDs. Showing just red and black colors make sense, and reducing the resolution also makes sense if they mean showing a small image with black around it. In September 2012 Google were granted a patent in which they suggest to reduce the image on a screen when the device is idle - this is basically the same idea which relies on the fact that black pixels on OLED displays do not draw power.

Merck - Advancing Display, Advancing LifeMerck - Advancing Display, Advancing Life