RKKK game is a vertical-screen color sorting puzzle mobile game. Players place continuously appearing colored blocks into the corresponding vertical columns, or temporarily put them into a holding slot; when a vertical column is filled with blocks of the same color and the colors match, that column is cleared and one point is added. When all placeable columns are full and the current block has nowhere to go, the round ends. The variety of colors increases as the game progresses, and difficulty gradually rises. Hold, undo, and hint are used respectively to temporarily store blocks, take back a move, and mark relatively safe landing spots. The rules are clear and a round is not long, making it suitable for casual players who enjoy color organization and forward planning.