When you have the HTML/Styles panel docked on the main program below the workspace and you click on the one of the little colored boxes in a style rule… for example…
The floating color palette window appears, and you can then click the eyedropper tool and select a color from anything on your website. This comes in handy when you want to say, match the color of text to a particular color in an image.
If the HTML/Styles panel is detached and placed on a second monitor, the eyedropper tool can no longer sample colors from the main program window. It seems the color selector is locked into the window of whichever monitor it appears on.
But it would be nice if the eyedropper could grab colors from either window, because it’s kind of useless when it’s trapped in the Styles palette on a second monitor. I suspect I already know what the devs @martin @gabby will say, which is that it can’t be done, but I figured I’d throw it out there anyway.