title: Qt quick ApplicationWindow 'color' for background color doesn't work
body: <p>I created a simple Qt quick application with a single main.qml, which is like the code below. The problem is the background color of window wasn't set to <code>#ffffff</code>, instead it's set to light gray (the default color of window on Windows I thought). The rectangle's color is set correctly.</p>
  
  <p>I'm using Qt Creator 3.3.1 (opensource) based on Qt 5.4.1 on windows.</p>
  
  <pre><code>import QtQuick 2.4
  import QtQuick.Layouts 1.1
  import QtQuick.Controls.Styles 1.3
  import QtQuick.Controls 1.3
  import QtQuick.Window 2.2
  import QtQuick.Dialogs 1.2
  
  ApplicationWindow {
      title: qsTr("Hello")
      width: 200
      height: 200
      visible: true
      color: "#FFFFFF"
  
      Rectangle {
          id: rectangle1
          width: 100
          height: 100
          color: "#ffffff"
      }
  }
  </code></pre>