Qt5 transparent is black without aero on Win7

When creating a transparent application window, the window appears as black instead of transparent. The problem happens on Win XP and Win 7 computers. If the aero theme is set it seems to work. However setting the aero theme individually on each computer is not a solution for deployment.

ApplicationWindow {
visible: true
width: 640
height: 480
title: qsTr("Hello World")

color:"transparent"

Rectangle

}