"Instant Eyedropper is a free software tool for webmasters that will identify and automatically paste to the clipboard the HTML color code of any pixel on the screen with just a single mouse click."
http://instant-eyedropper.com/
Να θυμίσω και το ColorPic που χρησιμοποιούσα εγώ παλιότερα (και αυτό free): http://www.dotnetzone.gr/cs/blogs/sfilip/archive/2006/02/04/9239.aspx