The orange cube in this game can move over grey and colored cubes. Only when the colored cubes are filled, it can slide over them: otherwise it will fall through them. The colored cubes only get filled when the vertical line in the timeline passes over the more vividly colored surfaces: clear red, clear yellow, clear green and clear blue. When the vertical line touches the pastel shades of these colors, the blocks in the screen get invisible again. Try it out and you'll see that the beginning's quite hard, but that it will become really fun after a couple of levels!
You can play this game both with the mouse and with the arrow keys/WASD. In the last case, click to jump.