if color is dark, will return a lighter one, otherwise darker

def contrast(self, color, step):
        """if color is dark, will return a lighter one, otherwise darker"""
        hls = colorsys.rgb_to_hls(*self.rgb(color))
        if self.is_light(color):
            return colorsys.hls_to_rgb(hls[0], hls[1] - step, hls[2])
        else:
            return colorsys.hls_to_rgb(hls[0], hls[1] + step, hls[2])