;; This will need a button to run it that is set to FOREVER, 
;;                             just like the GO button
;; A prerequisite to doing draw-cells, is that you did SETUP button first.
;;

to draw-cells
  
  while [mouse-down?]
    [ 
       ask patch mouse-xcor mouse-ycor
       [ ifelse pcolor = brown
          [ set pcolor red ]
          [ set pcolor brown ]
       ]
       display 
    ]
end