Steps:
1. Open the Qt Creator.
2. Create Project... -> Qt Quick Project -> Qt Quick Application, select "Qt Quick Components for Symbian". Default to finish.
3. Modify the code as follows:

import QtQuick 1.0
import com.nokia.symbian 1.0
Page {
id: mainPage
// Text

{ // anchors.centerIn: parent // text: qsTr("Hello world!") // color: platformStyle.colorNormalLight // font.pixelSize: 20 // }

//added begin
Grid {
columns: 3
spacing: 10
Rectangle

{ color: "red"; width: 50; height: 50 }

Rectangle

{ color: "green"; width: 20; height: 50 }

Rectangle

{ color: "blue"; width: 50; height: 20 }

Rectangle

{ color: "cyan"; width: 50; height: 50 }

Rectangle

{ color: "magenta"; width: 10; height: 10 }

}
Rectangle

{ anchors.centerIn: parent color: "red"; width: 100; height: 100 }

//added end
}

4. run the application.
5. Go to Design mode.
6. Highlight the last rectangle, click "Transparent" button in "Properties".

Actual Result:
QML designer is different from the run result.
"Transparent" button doesn't take effect, the rectangle becomes black.
Please refer to the attachments.