I am very certain, that the default color scheme of Ubuntu should NOT be changed. Please don't! Why, you ask?

1. Ubuntu has to keep being recognizable among the zoo of user interfaces. You have to recognize it on first sight. With Kubuntu, with it's blue theme, I'm afraid, this is not the case.
2. There can always be an evolution in the looks (I personally appreciated to move to lighter, more orange colors very much), but it should be done with a certain amount of consistency. A complete switch in the color scheme signifies something completely new - Windows can do that, because they bring out new versions only every couple of years, but Ubuntu is updated much more gradually, every 6 month.
3. What is - from a distance - recognized as a distinctly good design, normally does not look like what the great majority of people thinks (is made to think?) would be good looking. Example: Since the first iMacs they really had a sense for good design. Remember, when they introduced the first flat-panel iMacs, iBooks and iPods in that glossy white plastic look, everybody else thought (and some still do) that plastic housings had to be silver-colored in order to look like ... silver plastic? Now many other manufacturers try to imitate that (not always with huge success).
4. I tried other color schemes, but they always made me feel like I was using Windows, MacOS X or SuSE, and I don't want that - especially when I am NOT working with Windows, MacOS or SuSE. So I always came back.

So please, no hasty switches in the Ubuntu color scheme!