Game developer, Blizzard, announced at the Blizzcon, that players of its soon to be released Diablo III, will have the ability to customize all twenty of their character's skills with the use of five different colored Runestones.
Whereas in past iterations of the game, these runestones were placed in the sockets, and these stones are applied to the skills of a player's character. There are five colors---indigo, crimson, golden, obsidian and alabaster, which are able to change the skills of a character in different ways. The ways that the colors affect a character's skill follow a single theme. For instance, a crimson runestone will increase the damage that can be inflicted while a golden one decreases the damage.
These stones also come in different ranks of power. The higher the stones rank, the more dramatic the effect it has on the skill which it enhances.
For instance, when a barbarian uses a crimson stone to his whirlwind skill, the effect is to shoot bits of rock and gravel in every area, increasing area damage. The indigo stone allows the spawning of smaller whirlwinds that inflict direct damage to enemies. The obsidian stone makes the barbarian immune to immobilizing effects, while the golden stone reduces fury cost. Finally, the alabaster stone allows for critical strikes against enemies, confusing them and forcing them to attack their companions for a short time.
On the monk, a red runestone has the effect of increasing the area of damage to its sweeping wind skill by adding a flurry of blades. Indigo stones add fire damage to this kind of attack as well as expand the area of effect. An obsidian stone creates a persistent whirlwind around the character which harms enemies that come into contact with it. The golden stone increases spirit regeneration while the alabaster stone creates a powerful sandstorm, damaging enemies and pushing them back.
For other examples check the Blizzard website.