This is a brief guide to changing the color scheme of your Ubuntu desktop. It is subject to change as the little theme colorizer becomes more powerful and or easier to use.
1) sudo apt-get install gtk2-engines-clearlooks
(or grab it using synaptic)
2) Go to System->Preferences->Theme, Select Clearlooks. Hit Theme Details, Go to icons, select Human. You can also select a Window Border of your choice. You should end up with 'Custom theme' if you change anything. Select 'Save Theme' and give it a reasonable name. 'MyTheme' will be used for the remainder of this guide.
3) wget http://www.xmission.com/~callahan/cl...ustomizer-0.05
(or grab it using firefox).
4) python clearlooks-customizer-0.05 > ~/.themes/MyTheme/gtk-2.0/gtkrc
(Where 'MyTheme' is the name of your customized theme.)
This should bring up a somewhat primitive gtk+ applet. Select a reasonably light background color and a medium-dark accent color. The clearlooks options are already set to the defaults and can be safely ignored (or not, you won't break anything). Hit the 'Print gtkrc' button after your colors are selected.
5) Go back to System->Preferences->Theme. Reselect MyTheme to reload it.
6) Repeat 4) and 5) until your desktop suits your mood. If you don't like the results you can always reselect 'Human' from the Theme selector, or just create a new scheme.
Here are some quick example screenshots. In ClearCharcoal I have just picked a light grey background and a dark grey accent color off of the color picker's palette. In ClearSlash I typed in the slashdot colors (#FFFFFF and #006666).
Edit: bumped up clearlooks-customizer version number, added screenshots