9 Steps
TOOLS
Open settings
Click on general
Accessibility
Turn on "White on Black"
Now it's on. Give it a second......
You see the change.
Also works for iPad 1 & iPad 2 & iPod touch
An iPhone with white on black turned in
Do the steps again and take it off. Now back to normal
 iPhone
 Brain

How to use your iphone under direct sunlight

With this you can see under the sun easier than before. And it looks more cooler than before.