Oddly-colored fire is a sign that something magical is afoot. The different types of magic listed below are especially noteworthy because dragons regularly utilize them. However, because they are summoned from alternate realms of existence, the native fire will always defeat them. Natural fire, for example, can always be used to put out or defeat magical fire while in the mortal realm.
Fire summoned from Muspelheim. It becomes regular fire after spending time (usually only a few seconds, but it varies with the power of the spell) in the mortal realm, but when first summoned it does not require fuel or oxygen to burn and is not doused by water, though natural fire can easily beat it back. Until it is naturalized, elemental fire is easily absorbed by Void Iron, making many a mage's attempts to "cook an Inquisitor in his armor" end in catastrophe.
Green flame. Heals natural life (plant and animal), burns unnatural life (demons, undead). Sometimes summoned by Druids and other Spiritual casters. It can be doused by smothering or by natural fire, but not by water.
Also called Atar. Burns golden-white. Banishes darkness and destroys undead and demons. Fills the pure-of-heart with holy power and burns the souls of the wicked. Used by priests, spiritual mages, and light mages. It is more powerful in light places and can only be doused by shadow magic, water, or hellfire.
Burns deep, dark red and emits only a faint red glow. Scalds the souls of the living rather than their flesh, unless they are necromancers who have made demonic pacts, in which case they, like demons and undead, can pass through it unharmed. It is more powerful in darkness and can only be doused by light, water, or holy fire.
The opposite of normal fire. Burns black, emits darkness instead of light, feels cold, causes fear in most creatures, but does not cause real physical harm. It is not inherently evil and is not doused by light, but it can be put out in the same way as normal fire (water, smothering, or lack of fuel). Natural fire defeats it.
Burns blue-white, is cold and will eventually freeze objects in ice. It spreads, but can be put out with heat and/or natural fire, or by smothering, but not with water (which will freeze on contact with it).
Burns purple, emits relatively little light, floats in midair (weightless, doesn't require fuel to burn, although it will eventually fade out), does not burn or spread unless magically provoked. It does not last long in the natural world unless the caster sustains it, and it can be doused by water or natural fire, but not by smothering.
Summoned by a particular rune carved into the surface of any solid, inanimate object and then activated with a magic word. Burns with a bright light (its color determined by the exact rune), but creates no heat and does not spread. Can only be doused by casting a counter-spell or smashing the rune. Runic Fire is most often used by dwarves to light their underground homes, since it creates no smoke, though crafting a bright-burning rune requires great skill.