I don't intend to make this a "full blown something", but I recently looked at what the common CSS preprocessors do with colours, and they seem to kinda neglect it, so I decided to put my own routines on a page with a form so I can use it for whatever, and not just in the CMS I coded this for. But maybe it might be useful for others, too?
It's rather basic, and the "documention" isn't very nice either. But I still think it's possible to figure it out, just press "parse" with the pre-loaded example and compare input and output :) I already wouldn't want to miss it myself... once you make heavy use of variables for colors, changing the whole colour scheme by just changing 2-3 hues is awesome! Of course, you get what you put in -- you need to make use of little color variations, no just re-use colors unmodified, to get the most of it.
Anyway, if you have questions, suggestions or bug reports, I'm all ears :)
I'd be willing to share the (PHP) source, too... if you'd be willing not to laugh :D It's really first and foremost for myself, so the code is crummy and I'm cool with that; I just don't want to hog it, either.