Decide which color you want to
add and make it the foreground color.
Do one of the following:
Click the New Swatch button in
the Swatches palette. Alternatively, choose New Swatch from the
Swatches palette menu.
Position the pointer over an empty space in the
bottom row of the Swatches palette (the pointer turns into the Paint
Bucket tool), and click to add the color. Enter a name for the new
color and click OK.
Color selected from image (left), and added to Swatches palette
(right)
Note: New colors are saved in the Photoshop
preferences file so that they persist between editing sessions.
To permanently save a color, save it in a library.