Could you please post the model of your laptop? Is the system still under warranty? If so call Dell tech support and they can diagnose the problem. Also run diagnostics on your system. Restart the system and at the Dell splash screen start tapping F12. Run full system diagnostics paying special attention to the LCD results.

Thank you for your message. If your system is in warranty & need assistance with any part replacement.

For my reference, please click on the message tab next to your avatar– click “New Message” & search for my Dell username (Sreejith R) & send a private message with the service tag, registered name & email address.

How to find service tag.

I am not sure that the following page may help but there are a couple of suggestions posted there. If the screen does it in DOS that would seem to indicate a hardware problem with the screen, whether it passed diagnostics or not. The link below pertains to an external monitor but the fixes suggested would be the same for a laptop.

https://answers.microsoft.com/en-us/windows/forum/windows_10-hardware/screen-has-a-green-tint-to-it-windows-10/8724e339-0195-4f0d-affc-16759ddcbdf0?auth=1

This sounds like a problem with adaptive screen brightness (CABC).  (Note from an engineering perspective: when different current is applied to the LEDs lighting up the screen the tint can change.)

I'd look for an adaptive brightness setting and try turning it off.  Maybe in the BIOS or graphics/screen/display settings.

In some cases Dell has forced this on users with no way to turn it off.  They've also updated BIOS on some laptops to be able to turn it off - see post here and posts after it.

EDIT:  What version of Windows are you running?  Same question for BIOS and video driver.  Did you update any software/drivers recently, especially video/graphics related?