Defining Colors
If you want to redefine the foreground and background colors, use the
Eyedropper tool to select the foreground color, and then switch the
position with the background color, maybe by using the shortcut X, and
pick up the next color. But there is an easier way. First, define the
foreground color just as you’re accustomed to, but then define the
background color by holding the Alt/Option key. Instead of changing the
foreground color, you’ll redefine the background color with just one click.
Define foreground and background colors.