I've got a program that I wrote that can do the fractals, either using a palette of colors, or in monochrome. That background is the palette version, and the Mane 6 were rendered in monochrome and layered together using CrunchNugget's vector as a guide. After that, it was just playing with saturation/glow/lighting effects to make it look good. The process isn't particularly difficult, just time consuming. This wallpaper was built from nearly 50 layers.