Question: how does fire get its colour?

Thomas Smith answered on 23 Jun 2014:

I’ve been wanting to answer this question for a few days now! This is a great question, but the answer isn’t straightforward.

Let’s imagine a candle flame. The fuel for the flame is the wax. The wax contains a lot of carbon which when provided with enough heat will combine with oxygen in the air to form carbon dioxide (combustion).

Not all of the carbon is converted into carbon dioxide, some of it remains as very small dust-like solid particles of pure carbon. At room temperature, these particles would appear black. At higher temperatures, these particles will glow. The colour of the glowing is dependent on the temperature of the fire. For candles, the wax burns at around 1,000 °C, which corresponds to a yellow flame. Fires at hotter temperatures will appear to be more blue (e.g. a gas hob, or a bunsen burner).