If the black background is across Windows, switch Windows back to a light color mode:
- Select Start > Settings > Personalization > Colors.
- In Choose your color, select Light.
If the screen still looks white-on-black, also check contrast settings:
- Open Settings.
- Go to Accessibility > Contrast themes.
- If a contrast theme is enabled, turn it Off.
If needed, a Windows default theme can also restore the normal appearance:
- Go to Settings > Personalization > Themes.
- Select the Windows or Windows (light) theme.