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A good plugin to consider is the Designerator Color Plugin from the Designerator project. It contributes a Colors view as explained in this blog post. No need to install the whole software, the color view is in a separate feature that can be installed by itself.
The Sampler plugin could also be of interest. However it does not show a color picker dialog where one can select a color, it only has the color picker tool for selecting a color from the screen.
I have used this plugin called colors in both Galymeade and I just dropped into Galileo. http://www.eclipseplugincentral.com/Web_Links-index-req-viewlink-cid-1281.html you can copy the color code to/from clipboard or editor. Slider bar for coloring, color picker etc. I used it to edit css files on a recent project. Good Luck.