-It is passed a sample \c{game_state} in case it needs one, although
-currently no puzzle does need this. (In fact, colours are not
-reallocated when the game parameters change or a new game is
-started, so you can't reliably use this \c{game_state} to allocate a
-different number of colours depending on the game. It is probably
-actually a mistake to rely on this parameter at all. I ought to
-either remove it or fix it; probably the former.)
-
-The final parameter passed to this function is a front end handle.