Hi MagnusPF,
May you please take also a screenshot of the Colors page in Settings and share it to us here?
After changing or setting the colors settings of the device, were you able to do a restart on the device to make sure changes are applied? If not yet, kindly do so and see if still issue persists.
If in case issue persists, try to perform a force shutdown on the device by pressing and holding down the power button for 20 seconds just to clear its hardware cache then check if still the device displays in Dark mode even if it set to Light mode.
You may also run these steps below to make sure that the device has all its updated software and drivers needed:
1: Run Surface Diagnostic Toolkit
See: Fix common Surface problems using the Surface app and Surface Diagnostic Toolkit - Microsoft Support
The toolkit checks for updates and checks different parts of your Surface.
2: Check for Windows Update
Go to Windows Settings > Update & Security and select Check for updates
Make sure all updates need are installed including Optional updates
Kind regards,
Marrion