Sets background color

        Parameters
        ----------
        color : string or 3 item list, optional, defaults to white
            Either a string, rgb list, or hex color string.  For example:
                color='white'
                color='w'
                color=[1, 1, 1]
                color='#FFFFFF'

        loc : int, tuple, list, or str, optional
            Index of the renderer to add the actor to.  For example,
            ``loc=2`` or ``loc=(1, 1)``.  If ``loc='all'`` then all
            render windows will have their background set.

def set_background(self, color, loc='all'):
        """
        Sets background color

        Parameters
        ----------
        color : string or 3 item list, optional, defaults to white
            Either a string, rgb list, or hex color string.  For example:
                color='white'
                color='w'
                color=[1, 1, 1]
                color='#FFFFFF'

        loc : int, tuple, list, or str, optional
            Index of the renderer to add the actor to.  For example,
            ``loc=2`` or ``loc=(1, 1)``.  If ``loc='all'`` then all
            render windows will have their background set.

        """
        if color is None:
            color = rcParams['background']
        if isinstance(color, str):
            if color.lower() in 'paraview' or color.lower() in 'pv':
                # Use the default ParaView background color
                color = PV_BACKGROUND
            else:
                color = vtki.string_to_rgb(color)

        if loc =='all':
            for renderer in self.renderers:
                renderer.SetBackground(color)
        else:
            renderer = self.renderers[self.loc_to_index(loc)]
            renderer.SetBackground(color)