WordPress colorpicker save both hex and RGB

Thanks for your help Sally, here is the completed jQuery which pushes the RGB value to another field. Name of the RGB field has _rgb at the end.

jQuery(function() {
    var myOptions = {
        // you can declare a default color here,
        // or in the data-default-color attribute on the input
        defaultColor: false,
        // a callback to fire whenever the color changes to a valid color
        change: function(event, ui){
            var rgb = ui.color.toCSS( 'rgb' );
            var name = jQuery(this).attr("name");
            name="#" + name + '_rgb';
            jQuery(name).val(rgb);
        },
        // a callback to fire when the input is emptied or an invalid color
        clear: function() {},
        // hide the color picker controls on load
        hide: true,
        // show a group of common colors beneath the square
        // or, supply an array of colors to customize further
        palettes: true
    };
    jQuery('.color-field-custom').wpColorPicker(myOptions);
});

And here is what the custom field looks like below the color picker field.

<input type="text" name="destination_secondary_color_rgb" id="destination_secondary_color_rgb" value="<?php echo get_post_meta($post->ID, 'destination_secondary_color_rgb', true); ?>" />