Specifying foreground and background in qtquickcontrols2.conf has no effect

[Controls]
Style=Material

[Material]
Background=Purple

[Universal]
Background=Magenta

import QtQuick 2.7
import QtQuick.Controls 2.0

ApplicationWindow {
    width: 600
    height: 300
    visible: true

    Label {
        text: "Hello World"
    }
}