Pika

Pika (pronounced pi·kuh, like picker) is an easy-to-use, open-source, native color picker for macOS.

This application makes it simple to quickly find colors on the screen, in the format you need, so you can get on with being a speedy, successful designer. It lets you compare colors to quickly confirm WCAG compliance.

Both in your menu bar, and in the Touch Bar, Pika gets out of the way when you don't need it. You can choose from popular color formats like hex, RGB, HSB, or HSL, and seamlessly copy colors for other applications.