Use the Swatches Panel in Photoshop CS5
Use the Swatches panel in Adobe Photoshop Creative Suite 5 to store and retrieve frequently used colors. The Swatches panel lets you quickly select colors and gives you access to many other color options.
By using the panel menu you can select from a multitude of different color schemes, such as Pantone or web-safe color sets. These color systems are converted to whatever color mode in which you’re working.
To sample and store a color for later use, follow these steps:
To sample a color from an image, select the Eyedropper tool in the Tools panel and click a color in the image.
Alternatively, you can use any of the paint tools (the Brush tool, for example) and Alt-click (Windows) or Option-click (Mac).
The color you click becomes the foreground color.
If the Swatches panel isn’t already open, choose Window→Swatches.
Store the color in the Swatches panel by clicking the New Swatch button at the bottom of the Swatches panel.
Anytime you want to use that color again, simply click it in the Swatches panel to make it the foreground color.