Click to start (I don't know why it requires a click before listening to keyboard events.) Press 'n' for a new game. Press 2,3,4,5,6,7 or 8 to change the number of colors.
Two or more adjacent (right, left, above or below) squares of the same color will disappear when you click on them. Blocks will fall downward into the space. If an entire column is empty, it will slide over to make sure there are no gaps. The goal is to clear as many blocks as you can. There is no guarantee a puzzle is solvable.