I'm developing a web based mobile application and I was thinking about the default background color.
Do different color backgrounds use different amounts of battery life? For the best battery life should I choose black or white or some other color?
I would assume that because there's a back light behind the LCD then white would use the least amount of power because no pixels would have to be turned on, is this assumption correct?
i don't think the background-color has anny effect to battery lifetime (but if it does, black would be the "energy saving" mode)
For most devices the background colour you use has no effect on the battery usage. The backlight intensity isn't changed.
However on AMOLED displays the power consumption can vary "significantly". See the wikipedia page for details:
"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."
For LED displays the background color does not matter.
For AMOLED displays, which are used in many of the newer smartphones, a black background saves a significant amount of energy.
If battery life is the only concern, use a black background.
With ordinary LCD displays, the back light will consume far more power than any number of pixels. If your device has fixed brightness, you can pick any color you want, the difference in power usage will be miniscule.
On the other hand, if you can adjust the brightness, then what you want is the color scheme that gives the best contrast/visibility at the lowest possible screen brightness.
If it's an embedded device and you're in total control of features like screen brightness, this might be worth investing a little time. But if you're writing an app to run in an existing OS framework, something like overall display brightness probably won't be something you will be allowed to control.