ColorZilla

ColorZilla add-on features an online eyedropper, which makes it quite simple to get the exact value of a specific color. With ColorZilla you can get a color reading from any point in your browser, quickly adjust this color and paste it into another program. In addition to color picker, ColorZilla offers a DOM color analyzer which allows you to locate elements on the page that correspond to a given color and find out the CSS rules that specify a certain color. ColorZilla also features a online palette viewer that allows choosing colors from pre-defined color sets and saving the most used colors in custom palettes.