Normal Qubes are the same color as the Grid for that stage. Eliminate these Qubes before they reach the end of the Grid to avoid losing rows of the Grid.

MARKING NORMAL QUBES

To Mark a square on the Grid, press the Button. The Marked square will glow blue, signaling that the square is ready to Destroy the next Qube that rolls over that square. Press the Button again to Destroy the next Qube that rolls over that square.