Actually I was working on another image and played with mappings. While trying different merge modes I tripped over an interesting color effect. For it I should note that every layer is made with the same two-point-gradient, white and red brown. The color effect is a product of the 'Difference' merge mode, which can produce very nice colors but is hard to handle in my opinion. I'm not quiet happy with the center (in addition I lost some details during rendering) but couldn't find a effect which was halfway suitable.
Created with Ultra-Fractal, no postwork except subtle color enhancement.
FULL VIEW IS MUCH BETTER!
Edit: I changed the center - I'm still not really satisfied but I like it better in this way.