Rated 5 out of 5 stars
I have to disagree with SingleWolf, I find this addon to be much easiler than ColorZilla. As a full time programmer and designer, I need to copy matching colors on a daily basis. I used to take a screenshot of the page, open up a paint program, paste, and use the color picker. I love the simple inspector option, it simply displays a little square with the hex values of any area I mouseover which is exactly what I needed.
You should make the toolbar icon turned on by default, since at first I thought I had to go through the tool menu every time until I checked out the Addon's options to see that you can add rainbow to the toolbar.