Here's how you can invert the screen colors on your iPhone, iPad or iPod.
1. Go to Settings.
2. Go to General.
3. Go to Accessibility.
4. Tap the switch for Invert Colors.
Inverting the colors on your iOS device can make it easier on your eyes in certain kinds of lighting situations. If you find you don't like it, you can simply turn it off to go back to the usual color scheme.
But as with any device, there are tips and tricks and shortcuts that can help you get more from your iDevice investment. Here, in no particular order, I'm going to rattle through a list of tip and tricks that will help you be more productive when using your iPad and iPhone, whether you use it for work or play.More at ZDNet
Additional resources for iOS