Just thought I'd post this in case anyone else would want this sort of thing. I'm NO CSS ninja, I just clumsily hacked on it. The XDA icons are still yellow/brown, some of the links in the Dark Grey probably need tweaking.
Thanks to sickbox the bug in my CSS edits which make the top bar with User CP/FAQ etc disappear when you hover over the links is fixed!
The Stylish code is here, you'll need Firefox+Stylish Extension, Greasemonkey, or Opera to use it.
Blue - http://userstyles.org/styles/17609
Grey - http://userstyles.org/styles/17622
Dark Grey - http://userstyles.org/styles/17623
NEW! XDA 2010 Theme!
Blue - http://userstyles.org/styles/43606?r=1296614893
Above is my initial shot at converting the 2010 XDA theme to a blue. Once I work out the places to change, I can pretty easily add Greys etc. Help would be appreciated!
New!! XDA 2015 Themes
For the Dark theme
Blue - https://userstyles.org/styles/106066...015-dark-theme
For the default (light) theme
Blue - https://userstyles.org/styles/106068...15-light-theme
For 2015 I've only modified areas with wasted space and changed the font from Orange to Blue. It's still in beta a bit, I still have some clean up I'd like to do but I think it might be useful to some people.
Hope it's useful to some folks. I'm using it full time.