How to enable grayscale mode on your iPhone or iPad
iOS 8 offers a host of different accessibility features, most of which should come in handy to those users who have some kind of color blindness. One of these gets rids of colors altogether and allows you to view your display in grayscale, i.e. black and white. That's right, regardless of where you are, there'll be no colors whatsoever.
However, we should mention that turning this option will have no effect on your battery life, so don't expect an increase in this regard. Of course, the reason for this is the LCD display on your iDevice, which is backlit and doesn't consume less energy when only two colors are displayed, unlike on AMOLED displays which can benefit from such a limited color reproduction.
Here's how to turn grayscale mode on.
How to turn on grayscale mode on your iOS 8-running iPhone or iPad