Screen displays wrong colours

Everything is greyscale, black and white

Go to Settings > Digital Wellbeing & parental controls > Bedtime mode > Customise > Screen options at bedtime and turn Greyscale off .

Everything is negative, reversed colours

Go to Settings > Accessibility > Colour inversion and turn it off .

Tones, hues are different or missing

If the screen shows warmer tones than usual, check quick settings. If Night light is on, turn it off.
If certain colours appear diminished or their hues are different, go to Settings > Accessibility > Colour correction and turn Use colour correction off .

Background turned dark/light

Go to Settings > Display and turn Dark theme off .