LCD power consumption: color vs. B&W
By itself, an LCD being color or monochrome doesn't affect power consumption. Color LCDs are just monochrome LCDs with filters on the pixels to make them red, green, or blue. What will affect power consumption is:


Is the display backlit, and if so, how bright? Even a small LED backlight drawing 10 mA can easily overshadow the rest of the power consumed in the display.
How much computational effort are you using to keep the display refreshed? A high resolution graphical display may drive your system to have a faster processor, more memory, and higher clock speed than it would need for a simple character display. That increased performance comes with increased power consumption.


You have to look at the display options in the context of the system to make a determination of the ultimate effect on battery life.