Diablo III Runestones Detailed

Blizzard Entertainment's official Diablo III website has been updated with new details on the game's five different runestone types and how they can be used to further customize character skills.
There are five runestone types: Crimson, Indigo, Obsidian, Golden, and Alabaster. Each runestone affects skills differently. For example, adding a Crimson Runestone to a skill may enhance its damage, while adding an Alabaster Runestone might add a stun effect.

In addition to their color, runestones also come in different ranks of power; the higher a runestone's rank, the more dramatic its effect on the skill. Experiment, and discover which skill and runestone combination best suits your personal playstyle.
Five videos demonstrating how the different runestones directly impact character skills complement the article, so you'll want to check those out, as well.