If I remember correctly, onceI read that inverting colors or using a black background does not save battery power but actually increases it slightly (while the screen is backlit anyway, which is the main power draw).
Regardless, I agree one inverted color scheme would be not only be nice to have. Some people with reduced or impaired eyesight WILL find it easier to read white (text) on (blackground). And a properly designed will be even better than just using system-wide settings.
