iPad Pro colors appear negative

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]

"iPad Pro colors appear negative: my colour on the iPad Pro have gone very negative looking. I can’t seem to fix this. What has happened? Is it a common problem? Is it fixable and if so how?"

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What do you mean by "negative"?

Stopping Dimming Letters:

If they are becoming darker(dimming), then you likely have Auto-Brightness turned on.

Perform the Following:

1. Go to: Settings
2. Tap: Accessibility
3. Tap: Display & Text Size
4. Toggle Off: Auto-Brightness