code: def color_validator(input_str):
      
      try:
          assert input_str in VALID_OVERRIDE_COLORS + ['']
          return input_str
      except AssertionError:
          raise ValidationError(
                  'Expected colors are: ' +
                  ', '.join(color for color in VALID_OVERRIDE_COLORS) +
                  '. (Ctrl-C to exit)\n')
docs: A filter allowing only the particular colors used by the Google Calendar
      API
  
      Raises ValidationError otherwise.