This plugin provides a 3D visualization of all colors in an image. Colors are represented as RGB-values, hence each color corresponds to a point in color space. Histograms, although useful, represent only projections of the full 3D color distribution, hence important subtleties may remain hidden. The Color Cube plugin helps in detecting color clipping etc.
Color Cube lets you select a rectangular region or the entire image to be analyzed. You can spin the color cube and view it from any angle you want. You can also select the background color. Remember that Color Cube is an analysis tool, it will not alter your image. Version 4 adds an Opacity slider to vizualize the 3D color density.