QML ItemDelegate highlighted property not work

I want to customize highlight color in ItemDelegate. If I use default ItemDelegate with Material theme then all ok and color change when i hover over this item, but when I redefine background it breaks down and colors not change anymore.

MyItemDelegate.qml:

import QtQuick 2.11
import QtQuick.Controls.Material 2.4
import QtQuick.Controls 2.4
import QtQuick.Templates 2.4 as T

T.ItemDelegate {
    id: myItemDelegate
    height: 40     
    anchors.left: parent.left
    anchors.right: parent.right

    contentItem: Text {
            text: "Hello"
            anchors.fill: parent
            verticalAlignment: Text.AlignVCenter
            horizontalAlignment: Text.AlignHCenter
        }
    }

    background: Rectangle {
        anchors.fill: myItemDelegate
        color: myItemDelegate.highlighted ? "blue" : "transparent"
    }
}

Why highlighted property not work? And how I can customize this color?

The problem is simple, the highlighted property is not created from scratch, you must activate it, and the most common is that it has a binding with ListView.isCurrentItem, so you must update the currentItem:

MyItemDelegate.qml

import QtQuick 2.11
import QtQuick.Controls.Material 2.4
import QtQuick.Controls 2.4
import QtQuick.Templates 2.4 as T

T.ItemDelegate {
    id: myItemDelegate
    height: 40
    anchors.left: parent.left
    anchors.right: parent.right
    highlighted: ListView.isCurrentItem // <---
    contentItem: Text {
        text: "Hello"
        anchors.fill: parent
        verticalAlignment: Text.AlignVCenter
        horizontalAlignment: Text.AlignHCenter
    }
    background: Rectangle {
        anchors.fill: myItemDelegate
        color: myItemDelegate.highlighted ? "blue" : "transparent"
    }
}

main.qml

import QtQuick 2.9
import QtQuick.Controls 2.2

ApplicationWindow {
    visible: true
    width: 640
    height: 480
    title: qsTr("Scroll")
    ListView {
        id: listView
        anchors.fill: parent
        model: 20
        delegate: MyItemDelegate {
            MouseArea{
                anchors.fill: parent
                hoverEnabled: true
                onHoveredChanged: listView.currentIndex = index
            }
        }
    }
}