Please reference the photo here:
https://www.dropbox.com/s/48snki5swn98gwd/Dell%20XPS%2012%20touchpad%20problem.JPG
This shows what is happening to my brand new Dell XPS 12 touchpad/ultrabook right out of the box. Cleaning it doesn't help, nothing.. no matter what when you use the touchpad it discolors ... very ugly..
Jeff