def on_backend_state_changed(self, sender, backend_id):
        """
        Signal callback executed when a backend is enabled/disabled.

        @param sender: not used, only here to let this function be used as a
                       callback
        @param backend_id: the id of the backend to add
        """
        if backend_id in self.backendid_to_iter:
            b_iter = self.backendid_to_iter[backend_id]
            b_path = self.liststore.get_path(b_iter)
            backend = self.req.get_backend(backend_id)
            backend_name = backend.get_human_name()
            if backend.is_enabled():
                text = backend_name
            else:
                # FIXME This snippet is on more than 2 places!!!
                # FIXME create a function which takes a widget and
                # flag and returns color as #RRGGBB
                style_context = self.get_style_context()
                color = style_context.get_color(Gtk.StateFlags.INSENSITIVE)
                color = rgba_to_hex(color)
                text = f"<span color='{color}'>{backend_name}</span>"
            self.liststore[b_path][self.COLUMN_TEXT] = text

            # Also refresh the tags
            new_tags = self._get_markup_for_tags(backend.get_attached_tags())
            self.liststore[b_path][self.COLUMN_TAGS] = new_tags