Change Black background back to WHITE BACKGROUND

Make sure you are not in Dark Mode:

Settings > General > Display & Brightness

At the top of that page is a setting for Appearance. You have the option to select (always) Light, (always) Dark or Automatic which will switch automatically between Light and Dark according to the sunrise & sunset times for your locale.

See if this helps, Settings > Accessibility > Smart Invert or Classic Invert. Without a screenshot it’s hard to tell exactly the problem.

Opps I am rusty. I meant to say try Settings > Accessibility > Display and Text Size > Classic Invert. It’s the only way I know of to get the negative picture effect.

If the screen colours appear to be distorted or unnatural, you need to check some key Accessibility settings that are intended to compensate for specific colour-vision issues:

Settings > Accessibility > Display & Text Size

Ensure that all settings enclosed within the red box above are switched OFF/Disabled.

Otherwise, depending upon your installed version of iOS/iPadOS, you’ll need to look at your Dark Mode settings:

Settings > Display & Brightness > [Appearance]

On what, specifically?

Did two of us already post this same info above?