Maybe Nightshade Color splitter: http://polycount.com/discussion/131731/nightshade-blockout-v1-0-tool-for-creating-blockout-selection-maps-in-maya Or this one: http://eat3d.com/forum/tips-tricks-and-free-videos/rgbcmyw-splitter-photoshop-actions Not sure about reliability..they might introduce some errors.
I've been using the Nightshade Color Splitter linked above, for photoshop. It splits the colors into bitmap layers though, but I made an action that converts them to fill layers. Seems like the Nightshade script hosting is gone, but I kept a copy. Here is a zip containing it as well as the action I mentioned above.…