Here in Toronto we were rocked by a giant propane blast. It was so big that some thought it was nuclear dawn; it had both the characteristic mushroom cloud and a visible, expanding shockwave. Seeing the shockwave was awesome. Despite being located in a residential area (), the only known casualties are a missing employee and a firefighter. Anyway. That has nothing to do with my question. The explosion was a giant yellow-orange fireball, just like gasoline or any other. Yellow-orange fire and black smoke is an indication of incomplete combustion. Natrually, this is because the propane was being ignited as it was mixing with air. I was wondering what might happen in a hypothetical situation, if the air were first well-mixed with a large amount of propane. Would the fireball be blue? Invisible?