tor-android/orbotservice/src/main/res/drawable/toggle.xml

<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:state_checked="false"
        android:drawable="@drawable/button_off" />
    <item
        android:state_checked="true"
        android:drawable="@drawable/button_on" />
</selector>