Look into the centre (white point) and stare for a while. How many colours can you see altogether in the object? You should see a purplish circle... and the 4 rotating 'wings' are tinted green. Make sure you always keep focused on the centre. Once you've done this, read on... Are those four wings really green? Amazingly, they are exactly the same colour as the circle inside. Don't believe me? Well try following one of the wings round. You'll see that the colour matches the inner circle perfectly.