This plugin shows the color distribution within a 3D-color-space. Extensive documentation is available atwww.f4.fhtw-berlin.de/~barthel/ImageJ/ColorInspector/help.htm.
Color Inspector 3D is also available as a stand-alone program that uses ImageJ as a library. To run it, download ColorInspector3D.jar and double click on it. On Windows, Java 5.0 or later must be installed