Web developers like ColorZilla. ColorZilla is great, really great. But it has one issue: it's able to pick a color only inside the browser window, not anywhere on the screen or even the multiple screens you have. Since designers work with multiple types of sources, it is often necessary to get a color from outside the browser window and in that case ColorZilla can't help...
I was not really fond of writing a ColorZilla-like add-on for BlueGriffon myself since Mac OS X has /Applications/Utilities/DigitalColor\ Meter.app and my primary platform is OS X... But then I got an interesting message from a BlueGriffon user containing good, even very good I must say, arguments in favor of such an add-on. So I spent a few hours (roughly three) on it and here is the result. Honestly I already like it. It's not ironed yet and works only on OS X for the time being but the screenshot below will show you the best part of it : it works anywhere on all screens attached to your computer (see the crosshair cursor in the BlueGriffonEpubEdition icon on OS X desktop) ...

I think I can also make it work on Windows and Linux. And of course, it will be well integrated with the colorpicker in BlueGriffon. Stay tuned 
Update: the add-on now adds a new EyeDropper button to the color picker and is fully functional on OS X, Linux and Windows. Yay ! Will be released with forthcoming BlueGriffon 1.2.