Turns out there's another hidden little features in the new iPhone 3GS called the "White on Black" – and that's exactly what it does. It completely inverts the color scheme of your iPhone. The background on the home screen will be white, and the text will be black (as opposed to the typical white text on black background.) Furthermore, all of your native apps will have an inverted color scheme. Maps, instead of being beige and brown/green/yellow, becomes dark and blue. The feature also inverts the color scheme of photos. Even App Store apps will have their colors inverted.
This feature is made for people with vision problems, because for a person with good vision it's not a functional way to use your phone. Every color is inverted. If you've got bad eyes, or have trouble seeing things on the iPhone with the normal color scheme, then remember that this feature exists.
Also, it's a great way to play a trick on your friend. Especially if he's one of those that thinks he knows everything about his new iPhone 3GS.
When you take a screenshot it reverts back to "normal" in the photo automatically, which makes sense…screenshots are mostly for sharing purposes, so Apple realizes that most people don't wanna stare at an inverted color scheme.
1. Go to Settings
2. Go to General
3. Go to Accessibility
4. Turn on White on Black
That's all there is to it. Enjoy!