QT 5.9.4 - problems changing Label or Text color programmatically

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I have a BoxButton.qml defined as follows:

import QtQuick 2.9
import QtQuick.Controls 2.9
import "."

Rectangle {
    property int boxId: 0
    property string boxNo: "..."
    property string boxColor: "#efefef"
    property string labelColor: "#000000"

    signal btnClick(int boxId)

    width: 105
    height: 105
    radius: 5
    color: boxColor

    Label {
        id: label
        anchors.centerIn: parent
        text: parent.boxNo
        color: parent.labelColor
        font.pixelSize: 24
        font.family: Fonts.fontRobotoBlackLoader.name
    }

    MouseArea {
        anchors.fill: parent
        onClicked: {
            label.color = "#ffffff"
            btnClick(parent.boxId)
        }
    }

}

I am using it to create clickable boxes dynamically like so:

Component.onCompleted: {

	var boxes = DataProvider.fetchBoxes();
	var component = Qt.createComponent("BoxButton.qml")

	if (component.status === Component.Ready) {
		for (var n=0;n<boxes.length;n++) {
			var button = component.createObject(boxContainer)
			button.boxId = boxes[n].id
			button.boxNo = boxes[n].id

			if (boxes[n].isSystem) {
				button.boxColor = "#000000"
				button.labelColor = "#ffffff"
			} else {
				button.boxColor = "#cccccc"
			}

			button.onBtnClick.connect(handleBoxButton)
		}
	}

}

All boxes as created properly. Changing the boxColor property changes the background color of the boxes. The problem is that the same for the labelColor property doesn't work and the text color of the Label is not changing. The boxContainer is just:

Flow {
	id: boxContainer
	width: 800
	spacing: 20
}

Anyone experienced this strange behaviour?