If I understand it correct, there are 7 different colors:
blue (#4140FF, #58E0FF), green (#00aa30, #00ff00), magenta (#f000d0, #ff60dd), cyan (#009090, #00ffff), orange (#d06000, #ff9000), red (#E25551, #bbb) and gray (#bbbbbb, #bbb). In parenthesis are the htmll color-codes of the fill and border colors (I cannot use colors on forum posts 
)
They are used as follows:
- blue for “live games”. I think this isn’t used at the moment. Has someone seen that sometimes?
- green ranked 19x19 games one can accept.
- magenta ranked 13x13 games one can accept.
- cyan ranked 9x9 games one can accept.
- orange unranked games one can accept (any board size).
- red own challenges.
- gray not acceptable challenges.
If there is more than one open challenge for a point (time_per_move, rank) in the seek graph, the rectangle is bigger. (don’t trust the colors there, the color corresponds to at least 1 of the games, not necessarily all of them. Gray or red are only used if all of the games are either color).