QML - SystemPalette visible in all files

If you want use system colors create static variable in special singleton object.

// Style.qml
pragma Singleton
import QtQuick 2.11
QtObject {
     property SystemPalette palette: SystemPalette { colorGroup: SystemPalette.Active }
}

And then use it.

import QtQuick 2.0
Rectangle {
    color: Style.palette.highlight
}

Additional info here.