Colors & levels
  Color     Meaning    Rating      Equivalence
   Yellow           easy                     3 - 4                  3 - 6a
   Blue               moderate            3 - 5                  4c - 6c
   Red                difficult               4 - 6                  5c - 7a
   Black             very difficult       5 - 7c                6b - 8a
   White            extremely            7c+ - ...                  ...