docs: def find_nearest(self, hex_code, system, filter_set=None):
          """Find a color name that's most similar to a given sRGB hex code.
  
          In normalization terms, this method implements "normalize an arbitrary sRGB value
          to a well-defined color name".
  
          Args:
            system (string): The color system. Currently, `"en"`` is the only default
              system.
            filter_set (iterable of string, optional): Limits the output choices
              to fewer color names. The names (e.g. ``["black", "white"]``) must be
              present in the given system.
              If omitted, all color names of the system are considered. Defaults to None.
  
          Returns:
            A named tuple with the members `color_name` and `distance`.
  
          Raises:
            ValueError: If argument `system` is not a registered color system.
  
          Examples:
            >>> tint_registry = TintRegistry()
            >>> tint_registry.find_nearest("54e6e4", system="en")
            FindResult(color_name=u'bright turquoise', distance=3.730288645055483)
            >>> tint_registry.find_nearest("54e6e4", "en", filter_set=("white", "black"))
            FindResult(color_name=u'white', distance=25.709952192116894)
  
          """
  
          if system not in self._colors_by_system_hex:
              raise ValueError(
                  "%r is not a registered color system. Try one of %r"
                  % (system, self._colors_by_system_hex.keys())
              )
          hex_code = hex_code.lower().strip()
  
          # Try direct hit (fast path)
          if hex_code in self._colors_by_system_hex[system]:
              color_name = self._colors_by_system_hex[system][hex_code]
              if filter_set is None or color_name in filter_set:
                  return FindResult(color_name, 0)
  
          # No direct hit, assemble list of lab_color/color_name pairs
          colors = self._colors_by_system_lab[system]
          if filter_set is not None:
              colors = (pair for pair in colors if pair[1] in set(filter_set))
  
          # find minimal distance
          lab_color = _hex_to_lab(hex_code)
          min_distance = sys.float_info.max
          min_color_name = None
          for current_lab_color, current_color_name in colors:
              distance = colormath.color_diff.delta_e_cie2000(lab_color, current_lab_color)
              if distance < min_distance:
                  min_distance = distance
                  min_color_name = current_color_name
  
          return FindResult(min_color_name, min_distance)