Skala Color 2.0 (version history). OS X 10.8+ required.
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.
Skala Color automatically recognises colors copied to the clipboard, presenting them as a swatch that can be applied with a single click.
Dragging the hue and opacity sliders opens a 4× precision area, allowing fast targeting and fine tuning in a single mouse move. Version 2 adds random colour generation, Swift support, improved format parsing, and a new user interface.
Skala Color is free, to help spread the word about Skala, our upcoming design tool.