Someone has shared a very nice color picker utility called Colorette, which was written in AutoHotKey. The app description is at http://www.autohotkey.com/forum/topic69559.html and the EXE itself is http://www.autohotkey.net/~sumon/apps/colorette/Colorette.exe .
For an example of how to use Colorette with Revit, save the EXE to your Desktop and run it. Find a web page with the color you want to find, like http://www.jameshardie.com/homeowner/colorplus-palette.shtml , hover your mouse over the color on the screen and press Space on your keyboard.
Revit Learning Club Blog: How to Get a Color From Your Screen into a Revit Material