Choose Foreground and Background Colors in Photoshop CS5
At the bottom of the Tools panel reside the foreground and background color swatches. The foreground color is the color you apply when using any of the painting tools. The background color is the color you see if you erase or delete pixels from the image.
Choose a foreground or background color by clicking the swatch, which opens the Color Picker dialog box. To use the Color Picker, you can either enter values in the text fields on the right or slide the hue slider.
Pick the hue (color) you want and then click in the color panel to the left to choose the amount of light and saturation (grayness or brightness). Select the Only Web Colors check box to choose one of the 216 colors in the Web-safe color palette. The hexadecimal value used in HTML documents appears in the text field in the lower right corner of the Color Picker.
To quickly save a color, click the Add to Swatches button directly in the Color Picker.