Why, on a bunsen burner, does the flame go blue but when you turn it, it goes orange?

Question: Why, on a bunsen burner, does the flame go blue but when you turn it, it goes orange?
- Keywords:
  blue,
  bunsen,
  burner,
  flame,
  orange
Asked by saracallaway to James V on 29 Jun 2012.
- James Verdon answered on 29 Jun 2012:
  
  Hi sarecallaway,
  It’s about the amount of oxygen getting in to the flame. When the hole is open, the flame is blue. The full amount of air is getting to the flame, so it burns blue, which is the natural colour when gas burns. However, when the hole is burned, the gas doesn’t burn completely. This leaves particles of carbon in the flame (which should burn to produce CO2 if there was enough oxygen), which make the flame orange.

Question: Why, on a bunsen burner, does the flame go blue but when you turn it, it goes orange?