Converting stock .png graphics
For whatever reason, the pngs on the iPhone have some additional data in them that prevent the end
user from just opening the graphic and editing it. Apple also skews the color channels on the pngs.
To be able to modify these pngs, you must use a program that can convert them to a usable state.
It's my understanding the pngs are modified like this to make it easier/quicker for the iPhone to
process and render.
If you try to view stock graphic files in the firmware, you'll see they refuse to display.
I found this great program at Mac Update.com
that converts the .png into a usable format.
Decompress the download file and you will have an application to click on.
Drag the .png you want to convert into the program. Then click the Start button.
You will be prompted to select a location to save the converted .png to.
The program will let you know when it has finished the conversion. Click OK.
And here it is, a completely editable image. You do not need to do anything fancy to put this graphic
back onto the iPhone, other than making sure it stays in .png format.