Window opacity

Hello!

I am using Titanium 3.1.3, android.

I want to make a view when window background have opacity=0.6(user can see previous page) and in middle of window is my custom optionDialog .

<Window height="Ti.UI.FILL" height="Ti.UI.FILL" opacity="0.6">      
        <View  id="customDialog" backgroundColor="white" height="Ti.UI.SIZE width="Ti.UI.SIZE>
                      //my option dialog
                </View>
</Window>

But opacity have an effect upon my widnow and upon "customDialog". Could someone suggest me the way to cancel opacity for my customDialog view?