This page explores how go might be played with any non-negative integer number of colors.
There is an important distinction between number of players and number of colors. Traditionally, go is played with two players and two colors. Some simple variations of go change the number of players but not the number of colors; pair go is played with four players and two colors, and a person playing a game against himself is playing with one player and two colors. This page is concerned with the number of different colors of stones on the board, without regard to how many players play each color. For convenience, the examples on this page assume that each color is played by one player.
The game is over as soon as it begins. No moves are possible, not even passing or resignation. Every point is neutral and must remain so.
This is different than what is described at One Colour Go, which is really two-color go with stones that look the same.
At the beginning of the game, every point is neutral. On his first move, the one and only player claims the whole board. The player may pass at any time to end the game.
The only way to lose this game is to resign, and even then there is no winner. To get the highest score in most rulesets the player should move once, then pass.
With superko, the most moves the player can make before being forced to pass or resign is one less than the number of intersections on the board.
Two-color go has been discussed in some detail elsewhere in the library.
The obvious next step after playing with two colors is playing with three colors. (Here the third color will be red, marked by red squares in the diagrams.)
The order in which the players move becomes important. In these examples we will use the order black, white, red.
Mathematically, the komi for each player should be the difference between the winner's score and that player's with perfect play. It is likely that for most boards Black's komi is zero, White's is positive and Red's is greater than White's.
It is necessary to play more solidly than in two-color go.
Most of the time, a group left with two liberties at the end of a player's turn can be captured before he has a chance to play again. One can think of a group with two liberties as being in something like atari.
With the same color on both ends of a bamboo joint, Black can always defend against the cut, as in two-color go.
Black's bamboo joint can be cut by White and Red working together, if it's White's turn. On Red's turn, the cut fails. Also remember that if White attempts to cut, she has no guarantee that Red will cooperate.
In a three-color game, it's possible to capture stones of two different colour with one move. The stones can also be enclosed by two colours, because capturing happens when the group's liberties have been exhausted.
For an example of three-color go, see Three Colour Ongoing Game.
After making the leap from two to three colors, thinking about more colors isn't hard. There is no limit to the number of colors that can be used to play go.
Things start to get strange when the number of colors approaches and exceeds the number of intersections on the board. It would be something like two-color go on a 2x2 board?.
Most rulesets assume two colors. When playing go with numbers of colors other than two, it is necessary to use rules that make sense. Ideally, the rules for any multi-color go should still work when applied to two-color go.
In most two-color rulesets, the game ends after two consecutive passes. To make this work in multi-color go, we can end the game after n passes, where n is the number of colors.
Territory scoring becomes problematic with more than two colors, because it is not always clear who should get the points for the capture of prisoners. In this example, who gets the points? Is it White, because she took the final liberty, or is it Black, because he occupies more liberties? Should the points be split somehow?
For this reason, it is much easier to use area scoring when playing with three or more colors.
The basic ko rule doesn't apply well to three or more colors. Capturing a single stone that has itself just captured a single stone doesn't necessary lead to repetition. Superko works with any number of colors.
Is it meaningful to talk about non-integer numbers of colors? Negative numbers?
infraredux: I've never been a fan of adding more players to a two player game because often the game degenerates into politics; players A and B decide to gang up on C because C is winning. Is it interesting to have two players use multiple colors between them?