// Sets the opacity of the colour preview in response to moving the opacity slider
function webDesign_coloursDialog_updateColourPreview(opacityControlID, previewControlID) {
    var opacityControl = document.getElementById(opacityControlID);
    var previewControl = document.getElementById(previewControlID);
    if (opacityControl && previewControl) {
        var opacity = opacityControl.value;
        previewControl.style.opacity = opacity / 100;
        previewControl.style.filter = 'alpha(opacity=' + opacity + ')';
    }
}