(defun tty-color-256-define ()
  ;; colors 16-231 are a 6x6x6 color cube
  (let ((red 0))
    (while (< red 6)
      (let ((green 0))
	(while (< green 6)
	  (let ((blue 0))
	    (while (< blue 6)
	      (let ((code (+ 16 (* red 36) (* green 6) blue)))
		(tty-color-define
		 (format "color%d" code) code
		 (list (* (if (zerop red) 0 (+ (* red 40) 55)) 257)
		       (* (if (zerop green) 0 (+ (* green 40) 55)) 257)
		       (* (if (zerop blue) 0 (+ (* blue 40) 35)) 257))))
	      (setq blue (1+ blue))))
	  (setq green (1+ green))))
      (setq red (1+ red))))
  ;; colors 232-255 are a grayscale ramp
  (let ((gray 0))
    (while (< gray 24)
      (let ((level (* (+ (* gray 10) 8) 257))
	    (code (+ 232 gray)))
	(tty-color-define (format "color%d" code) code
			  (list level level level)))
      (setq gray (1+ gray)))))