The jquery-simple-color plugin has received a bunch of callback-related goodness thanks to jbergen. He’s also added a live preview option which displays the currently-hovered-on color.

onSelect:           Function to be called when a color is selected. The
                    hex code is passed into the function.
                     default value: null

onCellEnter:        Callback function that excecutes when the mouse enters a cell.
                     default value: null
                     returns: hex value

onClose:            Callback function that executes when the chooser is closed.
                     default value: null

livePreview:        The color display will change to show the color currently
                    under the mouse. The display will revert if no color is
                     default value: false

If any of this sounds useful, go grab v1.1.3 now :)