As most of us think fire exists only in one color, but it doesn’t. Yes, you heard it right. When somebody asks you what are different colors of fire? You think this might be a wrong question and eventually, you say only Red. But someone will say Orange and Yellow too. As the thermal temperature increases, it turns into blue, which has high temperature than those.
Energy radiated from the light comes as small packets. This packets of energy are called photons. And it is measured in quanta. Every color has certain frequency range and wavelength. The human eye can only see in a certain range, typically 430–770 THz in frequency range and 400 to 700nm in wavelength.
For example, you are burning something. Initially, it gets the color of red which has the higher wavelength. That means, there is an amount of quanta which can emit the Red color. If the quanta increases, it gets the energy to get the Orange color. As the thermal energy goes on increasing, it gets the colors like yellow, green and blue. So, ultimately we get blue which means, we are getting more thermal energy. In normal words, it is getting hot and hot.. This is different from the above concept.
Apart from that, we can change the color of the fire by adding different chemical substances. But this one is different from the above concept.
And blue colored fire is rich in oxygen, As it takes more oxygen to get more thermal energy.
The above image shows the different colors of fires in Bunsen burner.As we go from left to right the quantity of oxygen given gets increased. So in (4) finally it got the blue color.
If you want to get white colored flame, we should mix the combination of all colors in the exact ratio as Sun has.