app.js

var isTranslucent = true;

Ti.UI.setBackgroundColor('red');
var tabGroup = Ti.UI.createTabGroup({tabsTranslucent: isTranslucent});

tabGroup.addTab(createTab("Tab 1", "I am Window 1", "assets/images/tab1.png"));
tabGroup.open();

function createTab(title, message, icon) {
    var win = Ti.UI.createWindow({
        title: title,
        backgroundColor: '#000'
    });

    var button = Ti.UI.createButton({
        title: 'Toogle'
    });
   
   button.addEventListener('click', function() {
       isTranslucent = !isTranslucent;
       tabGroup.tabsTranslucent = isTranslucent;
   });
   
    win.add(button);

    var tab = Ti.UI.createTab({
        title: title,
        window: win
    });

    return tab;
}