Spot Color is a simple application that allows you to use the standard Mac OS X color picker as a stand-alone app. This allows you to quickly grab colors without having to be in an image editing app like Photoshop. Since it uses the built-in color picker, you can utilize the system wide color picker plugins and swatches.
Spot Color has been renamed to Hues. It has a bunch of new features and is available on the Mac App Store