Gods

Gods and their servants are not intrinsically good, but their general opposition to the forces of The Abyss sometimes makes people assume that they are. In truth, there are only three absolutes of divinity:

1. A divinity can draw power directly from worship, not by depleting the life-force of the worshipper, nor from material sacrifice, but from the very Existence of faith in their name.
2. A divinity can grant their worshippers access to divine Magic by manipulating the flow of creative force through The Firmament.
3. A divine entity cannot be truly slain by anything but another divinity; even a weak god is beyond the power of any Mortal, Celestial or Fiend to permanently destroy. 

Divine energy is an invisible force, but scholars of the divine and the celestial assign 'colours' to different forms of divine action, and by extension to the beings that take those actions.
Since The Creation of the Web of Fate, the barrier which divides the material and Elemental Planes from the outer realms, the natural state of divinity is to exist away from the mortal realm. Divinity which exists in The Firmament is characterised as blue. Blue gods offer and through clerics and miracles only, and blue celestials only enter the World in answer to the call of a mortal and to protect.
The vast majority of gods are blue, but since they are created on the material plane, all gods have the potential to remain there and seek to take a more direct hand in the World. Those who do are called red deities, and similarly, red celestials are those that exist in a permanent, material form. The presence of such power is potentially damaging to the world, and red deities are considered dangerous renegades.
Any god whose divinity gestates in a mortal form will instantiate in that form as a red deity. For this reason, such a mortal is called a Red Promise. Some gods and angels, however, choose to take on a material form for unselfish reasons. These are assigned the colour black, and the state is usually only temporary. Black celestials, never mind black deities, are the bane of the red, for they are equal in power to their quarry and Relentless in their pursuit. Even to mortals caught in their business, black divinity has a horror only righteousness can produce.
The last and rarest colour is white. White is the colour of the divine condemned to The Abyss; the colour of Dead Gods, and very little can kill a god. Slain celestials usually cease to be, as do gods slain by other gods. The white is reserved then for deities slain by mortals - almost an impossibility - and those that end their own life without also ceasing their existence.