anchor.diff:      
       (addch (char-code #\a))
       (addch (char-code #\b))
  -    (addch (char-code #\space)) ;; trying to write space will actually write the background char #\.
  +    ;; trying to write space will actually write the background char #\.
  +    (addch (char-code #\space))
       (addch (char-code #\space))
       (addch (char-code #\c))
       (getch)
  
positive.code: 
  ;; 190826
  (defun nctest6 ()
    (let ((scr (initscr)))
      (start-color)
      (init-pair 1 1 3) ; red(1) on yellow(3)
      (init-pair 2 2 7) ; green(2) on white(7)
      
      (color-set 1 (cffi:null-pointer))
      (addstr (format nil "color-set: red on yellow~%"))
      (getch)
  
negative.code:     (clear)
      (getch)
  
      ;; color-set (foreground) and bgkd write to the same global window variable.
      ;; here we se both at the same time
      (bkgdset (logior (char-code #\.) (color-pair 2)))
      (color-set 1 (cffi:null-pointer))
      (addstr (format nil "bkgd green on white, then color-set: red on yellow~%"))
  