It’s the Ghost Light!

This is one of the cooler effects in World of Warcraft. If you have the “Death Effect” turned on, this is what you get. Sort of a spirit world effect where everything is various shades of gray. I can’t remember if this option is on by default, but I doubt it since the description says that turning it on may impact performance. I know that when I’m all ghostified, I’m seriously concerned about my performance.

To enable (or disable) the effect, check the box labeled “Death Effect” in the Video Options under Shaders ( Video Options → Shaders → Death Effect ).