Fairy Tail Ep. 105

[Buffalobiian]

I was always under the impression that he was basically able to eat fire to regenerate his mana(or whatever Fairy Tail calls it), and then he just casts his Dragon Slayer spells which are all red fire.

Well yeah, that's basically what happened (and what I was trying to say).

On occasion he has shown to keep the quality of the flame he absorbed though. Examples include the black flame here, and the Golden flame of guilt by Jellal.