QQuickSystemPalette::QQuickSystemPalette(QObject *parent)
    : QObject(*(new QQuickSystemPalettePrivate), parent)
{
    Q_D(QQuickSystemPalette);
    d->group = QPalette::Active;
    connect(qApp, SIGNAL(paletteChanged(QPalette)), this, SIGNAL(paletteChanged()));
}

qt.core.qobject.connect: QObject::connect: No such signal QGuiApplication::paletteChanged(QPalette)

import QtQuick

Window {
    width: 300
    height: 200
    visible: true

    SystemPalette {}
}