Did you know that the OS X colour picker has a plugin framework? If not, I suggest you add these great colour pickers to your system-wide colour panel.
Panic’s Developer Color Picker is a custom color picker designed specifically for developers. Makes getting colors out of Photoshop/Acorn mock-ups quick and easy. Currently supports NSColor, UIColor, CGColorRef, CSS and HTML styles.
Hex Color Picker lets you edit and view hexadecimal color codes in the standard Mac OS X color panel.
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. It also automatically recognises colors copied to the clipboard, presenting them as a swatch that can be applied with a single click. The hue and opacity sliders let you quickly target rough values, then fine tune with 4× the precision.