When Does Toothless Turn Blue?

I know that there isn't probably much information about this but let's speculate. At the end of HTTYD 2 Toothless turned blue when he was fighting the big dragon and at that moment he was in alpha stage.

How did Toothless turn blue?

The torch has passages that allow the oxygen and acetylene to mix, react with one another, and produce the flame (acetylene and oxygen mixed in the right amounts will explode like those plasma blasts we see Toothless do). ... So Toothless glowing blue means that he's uber charged with firepower.

Why is Toothless fire blue?

Toothless' blue flame is said to be really hot so it's probably a mixture of dicyanoacetylene, cyanogen, acetylene or diacetylene gas that would react with the Potassium or Magnesium Nitrates to produce the purple color when it explodes.