As of Photoshop CS5 you can assign a keyboard shortcut to the Foreground Color Picker.
You can do so by opening the “Keyboard Shortcuts and Menus” window. Press Ctrl Alt Shift K (Mac: Command Option Shift K).
Then choose “Tools” and under “Shortcuts For” scroll down until you see “Foreground Color Picker.” You can then click on it to assign a keyboard shortcut.
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