Just to repeat my question from SO:
Ironic Sans: Ow My Eyes
they say it's not working for simple LCD
...using only the red pixels dropped the current use down to 35% of what the full color display was pulling...
WikiPedia - AMOLED:
For example, our measurement shows that a commercial QVGA OLED display consumes 3 and 0.7 Watts showing black text on a white background and white text on a black background, respectively.