ColorZilla is a Google Chrome and Mozilla extension that assists web developers and graphic designers with color related and other tasks.
ColorZilla allows getting a color reading from any point in the browser, quickly adjusting this color and pasting it into another program, such as Photoshop.
The extension allows zooming Web pages and measuring distances between any two points on the page. The built-in palette browser allows choosing colors from pre-defined color sets and saving the most used colors in custom palettes. DOM spying features allow getting various information about DOM elements.
Features
Multiplatform - Microsoft Windows, Linux, and Mac OS X
Eyedropper
Color picker
Page zooming
Palette viewer and editor (GIMP compatible)
History and Favorites palette
Page Pan
Displays element information (tag name, class, id, size)
Outline DOM elements
RGB, HSV, and HTML colors support
Auto copy
Launch DOM Inspector
Distance measurements