def *(other)
      raise ArgumentError, "Invalid argument given" unless other.is_a?(RGB)
      rgb = compound_by(other.rgb) { |a, b| [(a*b/255.0).round, 0].max }
      self.class.new *rgb
    end
def *(other)
      raise ArgumentError, "Invalid argument given" unless other.is_a?(RGB)
      rgb = compound_by(other.rgb) { |a, b| [(a*b/255.0).round, 0].max }
      self.class.new *rgb
    end
Color multiplication

 +other+ should be a Color object.
 It applies multiply compositing.