Each color flame inside the can has a different meaning behind it in the burn process to make charcoal for fireworks. When you first place the can into the fire, after about 5 minutes it starts smoking white. The white smoke is the moisture left over in the wood burning out. After all the moisture is gone, about 10 minutes, the smoke will turn a yellow and brown color. This is all the poison, impurities and oil burning out of the wood.
It will burn this color for about 5-10 more minutes. .
Once all the impurities have cleared the wood, the wood becomes combustible. The smoke will turn into a fire and will literally sound like a small rocket engine. Once the flame starts to slow down you have to get a wet wash cloth and throw over the hole in the can. You do this so no O2 (oxygen) gets inside the can. Oxygen will turn the charcoal into ash, ruining your whole batch of charcoal.
Yellow/Brown=oil, poison and impurities