Welcome to the Community. Try connecting an external monitor to the system to check if the display looks fine on an external monitor. It looks like an issue with the LCD.
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This is NOT screen damage caused by impact. My XPS15z does the exact same thing and I have seen many posts from many people having the same issue. From what I have heard, Dell will not cover this issue if the computer is out of warranty. That is BOGUS since it is obviously a flaw with the computer if it's happening to so many computers in the exact same spot.