My Fetish UIs (Nightfall and Classic) were specifically designed for rapid reskining. All the interface graphics have been consolidated into a few image files. I've also setup a dedicated namespace for all the styles, so none of the default style files are affected. All the window files have also been recoded for consistency.
Unless you're planing on a radical departure from the basic "windowed" style, starting with Fetish as a basis could save you some hassles.
The default UI scaters graphic elements across a dozen or more image files, is extreamly inconsistent in common item placement and size, and often applies styles directly to a window where a global style could be used.
I recently released 2 new themes for Fetish that took me a few hours to develop
