I often have to select colors from images for use in my HTML.  Taking a screenshot to use image editing tools to capture that color is inefficient, and the images I am sourcing aren't always coming from a web browser to be able to use browser extensions for that purpose.  That's why I like a desktop tool:

Instant Eyedropper is a free software tool for webmasters that will identify and automatically paste to the clipboard the HTML color code of any pixel on the screen with just a single mouse click.

From Instant Eyedropper

This is a pretty handy tool for Windows that quickly captures colors from anywhere on the screen, and is significantly faster than other color pickers I've used in the past.