Tip#89: Auto-update background/foreground color relationship when using eyedropper
Keep relationship between foreground and background colors when using eyedropper. In Photoshop click Link button next to color swatches on MagicPicker color wheel panel and then use eyedropper.
Background color will update automatically. So for example you can always have complementary color in the background swatch.
Note that you can assign a keyboard shortcut to the Link functionality.