If you are trying to show someone at an Apple store that your screen has the inverted black problem, you may also want to try this test:
http://techmind.org/lcd/greyscale.html
The block marked "00" (on the far left) should be the blackest black. If you have the inverted black problem, the block marked "10" will be blacker than the block marked "00" (on my defective display, the block marked "00" was a lighter greyish greenish color in comparison to the block marked "10").
This is easy to see if you pull up the same link on two Iphones (assuming the other Iphone has a non-defective screen). I had a 8GB Iphone with a good screen and then purchased a 4GB Iphone for my wife that had a bad screen. I saw this link on another site, and it helped me explain the problem to the manager at the Apple store, so I thought I would share it.