Hello rhusvik,
We understand the display on your iPhone was inverted to display only black and white colors. You've done a great job trying to reverse this on your own.
When you go to Settings > Accessibility > Display & Text Size > Color Filters, what do you see here? If you have Color Filters enabled, what happens when you disable it completely?
For additional information on Color Filters, please see how to Use display and text size preferences on your iPhone, iPad, and iPod touch.
If this resolves what you are seeing, we'd also recommend checking for any Accessibility Shortcut that might have enabled this feature. If needed, you can learn About the Accessibility Shortcut for iPhone, iPad, and iPod touch.
Cheers!