def to_array(color_model = :rgb)
      color_model = color_model.to_sym unless color_model.is_a? Symbol
      if color_model == :rgb
        array = [self.red, self.green, self.blue]
      elsif color_model == :hsl
        array = [self.hue, self.saturation, self.lightness]
      else
        raise(ArgumentError, "Argument must be :rgb or :hsl")
      end
      array
    end
def to_array(color_model = :rgb)
      color_model = color_model.to_sym unless color_model.is_a? Symbol
      if color_model == :rgb
        array = [self.red, self.green, self.blue]
      elsif color_model == :hsl
        array = [self.hue, self.saturation, self.lightness]
      else
        raise(ArgumentError, "Argument must be :rgb or :hsl")
      end
      array
    end
Return an array representation of a {Color} instance,
 @param [Symbol] model the color model, should be :rgb or :hsl
 @return [Array] an array of component values