Hello SabrinaMCC-CRA,
It sounds like the colors are inverting specifically on the Lock Screen, is that right?
If so, first ensure that both Smart Invert and Classic Invert are disabled at Settings > Accessibility > Display & Text Size. This page can help to go over the topic: Use display and text size preferences on your iPhone, iPad, and iPod touch - Apple Support
If those are both disabled, try heading to the following:
- Settings
- Accessibility
- Per-App Settings
- If Home Screen is here, tap on it
- Disable the Invert options here
Cheers.