If you see a spiderweb in the right light, you will see a spectrum of colours, and if you move around you'll see different colours. Why?
You see the colours because of defraction: White light contains all of the colours in the spectrum, and when it hits the spiderweb, the colours scatter. It looks like the colours change when you move because you are blocking out some of the spectrum.
Our winner isSandy MacLeod of Dartmouth