How to use the nglview.color.COLOR_SCHEMES function in nglview

self.colors = {}
        self.view._remote_call('setSize', target='Widget',
                               args=['%dpx' % (xsize,), '%dpx' % (ysize,)])
        self.view.add_unitcell()
        self.view.add_spacefill()
        self.view.remove_ball_and_stick()
        self.view.camera = 'orthographic'
        self.view.parameters = { "clipDist": 0 }

        self.view.center()

        self.asel = Dropdown(options=['All'] +
                             list(set(self.struct.get_chemical_symbols())),
                             value='All', description='Show')

        self.csel = Dropdown(options=nglview.color.COLOR_SCHEMES,
                             value='element', description='Color scheme')

        self.rad = FloatSlider(value=0.5, min=0.0, max=1.5, step=0.01,
                               description='Ball size')

        self.asel.observe(self._select_atom)
        self.csel.observe(self._update_repr)
        self.rad.observe(self._update_repr)

        self.view.update_spacefill(radiusType='covalent',
                                   radiusScale=0.5,
                                   color_scheme=self.csel.value,
                                   color_scale='rainbow')

        wdg = [self.asel, self.csel, self.rad]
        if self.frm: