I would like to add a small correction to what Todd said.
At present Telerik RadEditor does not use RadColorPicker for its own color pickers. The editor is implemented for maximum performance and has its own version of the toolbars and its own color picker - scaled down and tuned only for being used in the editor (and not in variety of scenarios such as RadColorPicker and RadToolBar, for example).
The article provided by Todd is just the thing you need, however.
Please note, that while the color picker dialog there currently uses a color picker from Yahoo Widgets, we will rework it soon to use Telerik RadColorPicker. The RadColorPicker just got a second mode for picking colors - using 3 RadSliders, and we plan to soon introduce a third mode (also allowing for millions of colors).
the Telerik team