Each of the 64 pieces on the board above has an inner color and an outer color. Arrange the pieces above so that no two pieces in a row or column have the same inner or outer color.

Pieces may be dragged.

Inner colors may be toggled by typing i.

Outer colors may be toggeled by typing o.

Reset the board with r.

Undo moves with <; redo with >.

Visual hints are toggled with h. (Complete rows and columns are wider and taller than those that are not complete.)