Shoes.app :width => 150, :height => 150 do

  def toggle_rectangle_color color
    fill  color
    rect  0, 0, 150, 150
  end

    every(3) do
      case @color
        when blue
          clear {toggle_rectangle_color red}
          @color = red
        when red
          clear {toggle_rectangle_color blue}
          @color = blue
        else
      end      
    end
  @color = blue
  toggle_rectangle_color @color
end