I had heard that you can save power by using a black background instead of a coloured background. Is there any evidence that this saves power on people's monitors?
Is this a way that we can cut down on energy consumption (millions of users times milliwatts add up over time). It could also affect battery life on mobile devices.
No, it doesn't save power. http://googleblog.blogspot.com/2007/08/is-black-new-green.html
You can save power by turning down the brightness of your screen, or (obviously) by turning it off when you're not using it.
You would expect a black background to save power on a purely emissive display such as actual LED (as opposed to LED-backlit LCD), OLED or plasma. CRT I'm not sure about because I don't know exactly how it dims the electron beam.
However, the most common type of computer monitor these days is LCD, which as others have pointed out, actually uses energy changing the LCD to absorbing mode to make pixels black.
There is some power savings with a large CRT. I had a 19" CRT (now sitting in the bottom of a closet due to being replaced by a 22" widescreen LCD) hooked up to a UPS, and with the computer in an idle state showing a mostly black screen would have 2 of the 5 load indicator LEDs lit, but a partially white screen would bump it up to 3.
Now, could this be called "considerable"? Not likely. But it is more than none.
