Also known by the name of "Frostfire", this white and black colored flame is a highly advanced and spiritual technique. Accessed through similar means of Lightning Generation, but slightly altered, certainly more difficult and likely more dangerous to the if they fail the process.

For a Firebender to create lightning, they must separate the Yin and Yang (positive and negative energy) within themselves. And as protons and electrons strive to an equal charge, the pos and neg energy desire to be reformed to attain equilibrium once more. They then crash back together to create lightning.

However, to use the true "Cold-blooded Fire", the caster must make the Yin and Yang energy fully positive and fully negative. I'm sure you all know what the Yin and Yang icon looks like, but the small dot of light in the dark and vice versa, you must swap them out to make each half one solid color. One white half and another black half, with no intermingling.

And then with this unnatural energy of pure positive and pure negative, it inverts the properties of your fire to be a freezing cold as opposed to a scorching heat. This type of fire bending is boosted by the Full Moon instead of Sozin's Comet due to its polarized nature.

I felt like there'd be more to write when I thought of this-