Here's the answer:
Zone 1 and zone 3 are filled with gaseous candle wax where there is not enough oxygen to burn the wick. The bottom of the wick is "wicking" melted wax and is below combustion temperature. The tip of the wick, however, is usually in zone 2 where the gaseous envelope of wax comes in contact with oxygen and thus promotes burning, producing the orange glow.
