Hi black0,
I request you to run a test on the display. This test will help in diagnosing if the issue is with the LCD panel or with the controller. If the colors are displayed across the screen without a problem then the issue lies outside of the LCD. To test the display shut the system down, next press and hold the letter ‘D’ on the keyboard and press the power button. This will initiate diagnostics on the display. Check the status of the display and please revert.
Also connect an external monitor and check the behavior. You may leave the system in the BIOS screen for a while and observe the behavior. To go to BIOS restart the system and at Dell logo tap the F2 key every two seconds.
Revert with the status.