Quote Originally Posted by Darth
But if he JUST emptied himself of his Dragon, where is he getting the Dragon that he's adding a second later?

I could see if it later, after he'd rested, but whats the significance of sacrificing all your mana to do something if it comes back instantly?
Because he's all revved up.

There's nothing to indicate that God's flame must remain God's flame (or black) once Natsu has absorbed it. It makes sense for Natsu to be able to convert it really (though whether or not you'd want to since it's stronger is another question). Natsu's always been absorbing other people's flames and making them his own.