Gaze at the central cross and watch the patches disappear. With should see a strong greenish colour whenever the violet patch has disappeared. If you are lucky the purple patches will disappear and you'll just see a moving green spot.
although its nothing new, but more interesting stuffs
i dont know the history, who created that!!, i have read, the palace in andulusia had these type of stuffs on the walls and ceilings, so the christian natives were amazed by creative work of muslim Spaniards