To switch Windows to a light background:
- Open Start > Settings.
- Go to Personalization > Colors.
- Set Choose your mode to Light.
If it switches back to dark after a few seconds, check whether PowerToys Light Switch is enabled:
- Open PowerToys Settings.
- Go to System Tools > Light Switch.
- Turn off Enable Light Switch.
- Then return to Start > Settings > Personalization > Colors and set Choose your mode to Light.
Also check Accessibility > Contrast themes and turn off any active contrast theme if the display still appears white-on-black.