Screen displays wrong colors
Everything is grayscale, black and white
Go to Settings > Digital Wellbeing & parental controls > Bedtime mode > Customize > Screen options at bedtime and turn Grayscale off 
Everything is negative, reversed colors
Go to Settings > Accessibility > Color and motion > Color inversion and turn it off
Tones, hues are different or missing
- If the screen shows warmer tones than usual, check quick settings. If
- If certain colors appear diminished or their hues are different, go to Settings > Accessibility > Color and motion > Color correction and turn Use color correction off
Background turned dark/light
Go to Settings > Display and turn Dark theme off