Dragon's Flame, Magical?

[Dwarven Warrior]

Originally Posted by Alfirin

But heat alone can't make fire turn green; the color/heat pattern for fire is the same one (quite logically) for magnitute of stars. From coolest to hottest it goes- red,orange,yellow, white, blue-white. Fire can't burn green witout help.

But no other dragon other than Smaug has ever done this. I'm scurrying through my LotR books here, and I can't find anywhere else that it says that.