I found it on my 32gig 3rd generation iTouch so i'm not sure if it works for any other generation or type of ipod. It didnt show up on my brother's iTouch which is older so you may need a 3rd gen, not sure.
Go to Settings -> General -> Accessibility -> White on Black -> ON
I thought it looked damn cool and thought i'd share my discovery with ya'll.

This isnt the coolest looking picture but its the only one i could find. A lot of the other screens you can go to look a lot cooler. It also makes some games look 10 times cooler.