Monochromatic chess

Monochromatic chess is a chess variant built on one governing constraint: a piece that begins the game on a black square must remain on black squares for the rest of the game, and a piece that begins on a white square must likewise stay confined to white squares throughout. Because an ordinary knight always moves from a square of one color to a square of the other, the variant cannot function with unmodified knights, so its rule sets either allow knights to make a double jump that lands back on a same-colored square or replace them outright with a longer-range leaping piece. The single-color restriction also reshapes pawns, which become limited to captures and their initial two-square advance, and it narrows castling, which stays legal on the kingside once the color-locked knights are removed from the board. These constraints produce endgame positions that would be drawn or ongoing in orthodox chess but become checkmates or stalemates here, since only one bishop per side can ever threaten a same-colored enemy king, a property that has made the variant a favorite tool for logicians such as Raymond Smullyan in composing deductive chess puzzles.