Skala Color, a Mac color picker by Bjango.
I use this everyday and love it. Simple but very powerful. Hit the source link below for a full review.
From Bjango:
Skala Color is a compact and feature-rich OS X color picker that works with a huge variety of formats, covering everything you’re likely to need for web, iOS, Android, and OS X development — Hex, CSS RGBA, CSS HSLA, UIColor, NSColor and more.
source: MacStories post