Scale R, G and B parameters
        :param new_max_value: how much to scale
        :return: a new ColorRGB instance

def scale(self, new_max_value=1):
        """
        Scale R, G and B parameters
        :param new_max_value: how much to scale
        :return: a new ColorRGB instance
        """
        f = new_max_value / self.max
        return ColorRGB(self.r * f,
                        self.g * f,
                        self.b * f,
                        max_value=new_max_value)