anchor.diff:  
       ;; -1 are not the terminal colors, but the (assumed) default colors.
       (init-pair 3 -1 -1)
  -    
  +
       ;; as soon as one of the assumed default colors is -1,
       ;; the other is also set to -1 for unrendered characters.
       (addch (char-code #\a))
   
       ;; when we reference 5 -1 in a color pair, then the mixed pair works.
       (addch (logior (char-code #\d) (color-pair 3)))
  -    
  +
       (addch (logior (char-code #\b) (color-pair 1)))
       (addch (logior (char-code #\c) (color-pair 2)))
  -        
  -    (refresh)
  -
  -    (getch)
  -    
  +
  +    (refresh)
  +    (getch)
       (endwin)))
   
   ;; 200517
  
positive.code:     ;; we can actually use the default color pair, but have to give it another color pair number
      (addch (logior (char-code #\d) (color-pair 2)))
  
      (color-set 0 (cffi:null-pointer))
  
      (addch (char-code #\e))
      
      (refresh)
  
      (getch)
      
      (endwin)))
  
  ;; 190901
  (defun nctest8 ()
    (let ((scr (initscr)))
      (start-color)
  
  
negative.code:     
      (addch (char-code #\a))
      (addch (char-code #\b))
      ;; trying to write space will actually write the background char #\.
      (addch (char-code #\space))
      (addch (char-code #\space))
      (addch (char-code #\c))
      (getch)
  