Following up on Macworlds article about the Mac OS X color picker, adriann noted on macosxhints that they left out the most juicy part.

Allow me to take over the subject and add a small bit to it regarding Photoshop availability of this tip.

The story on macosxhints was about the feature of colorpicker that you can aparently add an image to it to pick colors from. Very useful if you have created a color palette you want to work with or if you want to use the colors from a corporate identity guideline.

Just open color picker in any application (such as TextEdit) by pressing Apple-Shift-C (Cmd-Shift-C). And choose the little icon with a mini landscape. Now go to the Palette drop down menu and select New from File.... Select the image that you will use as a reference and voila you have a handy color picker available at all times.

This color picker is available accross all applications, including Photoshop, but you need to do a custom setting to enable it. Open your Photoshop General Settings... (Apple-K) and set the color picker to Apple. Now the little color reference is even available in PS.

Here are two related posts about the built in Digital color meter and how to use the eyedropper outside Photoshop if you want more colorpicker tricks.