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Why a candle flame burns yellow, while a highly-oxygenated gas-fuel flame burns blue

Why a candle flame burns yellow, while a highly-oxygenated gas-fuel flame burns blue?

Answer: The most important factor determining color of the flame is oxygen supply and the extent of fuel-oxygen pre-mixing, which determines the rate of combustion and thus the temperature and reaction paths, thereby producing different color hues. 

In case of candle, it is an incomplete combustion and the flame temperature is not high. This gives a yellow flame. While a highly-oxygenated gas (e.g. ethyne) flame burns blue because of complete combustion raising a very high temperature.
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