There is a convenient online color picker at ColorPicker.com. It is quick and easy to use when you are online and don’t want to take the time to fire up your favorite image editing software.
I created a tutorial using this color picker to learn Photoshop’s color systems and how those systems relate to Photoshop’s primary, secondary and tertiary colors.
Series Links
“How To” Series: Photoshop’s Color Tools and Systems
Learning Photoshop Colors – A Color Picker Tutorial
Tutorial: Using Photoshop’s Color Selection Tools
How to Create Your Own Photoshop Color Wheel