If you selected a colour mode, it will resume outside of night hours.
Your phone can automatically filter out blue light and adjust screen colours to warmer tones at night, making it easier to view and read in dim light. You might even fall asleep more easily.
Touch Schedule, then:
To adjust filter intensity, open Quick settings, press and hold 
To temporarily switch back to regular colours from amber, open Quick settings and turn off 
To stop automatically changing to amber, select Settings > Display > Night light > Schedule > None.
To help you wind down at night, your phone can change to greyscale (black and white).

To temporarily switch back to regular colours from grayscale, open Quick settings and touch 
To stop automatically changing to greyscale at night, go to Settings > Digital Wellbeing & parental controls > Bedtime mode > Customise > Screen options at bedtime and turn Greyscale off 
If colours don't appear as you expect, troubleshoot the issue.