Usually, only rarely reaches visible-green stage. Occasional natural occurrences, which would be tamed by a creature who lived off of aer. Normally,use of blastia - world's form of magi-tech - would cause the occurrences more often, but still rare enough that it is vaguely known and little more. Red requires intentional disregard for safety or a great deal of improper use, as well as preventing the aid of the creatures.