turtles-own [
draw
]

to setup
    clear-all
    crt 36
    ask turtles [
      set heading who * 10
      set color who * 5
      pen-down
      set draw 1
       ]
end

to go
   ask turtles [
      fd 1
      set draw 1 - draw
      ifelse draw = 0 [
        pen-up
      ]
      [
        pen-down
      ]
   ]
end

to rev
  ask turtles [
       set heading heading + 180
  ]
end