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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_vertex_colors(self, indexed=None):
 """Get vertex colors Parameters indexed : str | None If None, return an array (Nv, 4) of vertex colors. If indexed=='faces', then instead return an indexed array (Nf, 3, 4). Returns ------- colors : ndarray The vertex colors. """

        if indexed is None:
            return self._vertex_colors
        elif indexed == 'faces':
            if self._vertex_colors_indexed_by_faces is None:
                self._vertex_colors_indexed_by_faces = \
                    self._vertex_colors[self.get_faces()]
            return self._vertex_colors_indexed_by_faces
        else:
            raise Exception("Invalid indexing mode. Accepts: None, 'faces'")