All I do is use the 'Render Clouds' filter with different colors in the fore and background. There's usually tweaking, though, whether through Hue/Saturation, or else (in this case) the repeated application of the Difference Clouds filter on top of it.
The title is actually a reference to Shuyin's gradual degeneration from just wanting to destroy his city's enemies to being singlemindedly bent on wiping the planet clean of life. A thousand years of hell can make a huge difference in someone.
ahhh! I'm beat, your pyreflies are far better then I could ever *hope* mine could be. Mwuheehe, your's are just BEAUTIFUL, love the color scheme, I also love how you drew Shuyin, it's not a direct copy of the character art like a lot of people I know, it looks very original, but I could tell right off it was Shuyin, mwuhehe, your shading is absolutely gorgous as well.... Much love to you!