Monochromatic chess
| a | b | c | d | e | f | g | h | ||
| 8 |      | 8 | |||||||
| 7 | 7 | ||||||||
| 6 | 6 | ||||||||
| 5 | 5 | ||||||||
| 4 | 4 | ||||||||
| 3 | 3 | ||||||||
| 2 | 2 | ||||||||
| 1 | 1 | ||||||||
| a | b | c | d | e | f | g | h | ||
Monochromatic chess is a chess variant created by Raymond Smullyan, in which the initial board position and all rules are the same as in regular chess, except that pieces which begin on a black square must always stay on a black square and pieces which begin on a white square must always stay on a white square. This means that knights can never move, castling can only be done on the King's side, and pawns can only move by capturing or by advancing two squares for their first move. A stalemate occurs if a player's King is not in check but the player nevertheless has no legal moves under the rules of the game. Similarly, a checkmate occurs if the King is placed in check and the King has no legal moves under the rules of the game. This means that certain board positions in regular chess which would not result in the end of the game can be checkmates or stalemates in monochromatic chess. For example, each player has one bishop for which it is impossible to obtain checkmate with just this bishop and a king, while it is impossible with the other bishop along with the king, since only one bishop is capable of threatening the King of the opposing side.
This variant is used mostly in chess problems. Smullyan's example ask: What color is pawn g3 - white or black? Answer is black, white king can walk from e1 only with castling (O-O) and then g1-h2-g3-... so Pg3 can't be white.
In opposite bichromatic chess, only moves that change square color are legal. Hence pawns cannot capture and bishops cannot move.