This is a tool that I have found very useful when designing web portals,

Run the program to begin and simply point to a color.  The screen will display the hex, RGB, HTML, CMYK and HSV values of that color.

You can then use these values to reproduce the selected color for your website or document.  Pixie will also show the current coordinates of your mouse pointer.

This is a free program and can be found at http://www.nattyware.com/pixie.php