Gcolor2 is a GTK2 color selector to provide a quick and easy way to find colors for whatever task is at hand.
Does exactly what it claims to. It definitely beats taking a screenshot and then firing up something heavy like GIMP just to figure out what color a given pixel or object is. GUI designers will likely appreciate this little tool the most, but I would recommend it to any sort of graphic designer on Linux. You never know when it could come in handy.