Emacs: change cursor color during active repeat-mode commands

repeat-change-cursor-color.el

(let ((orig (default-value 'repeat-echo-function))
	rcol ccol in-repeat)
    (setq
     repeat-echo-function
     (lambda (map)
       (if orig (funcall orig map))
       (unless rcol (setq rcol (face-foreground 'error)))
       (if map
	   (unless in-repeat		; new repeat sequence
	     (setq in-repeat t
		   ccol (face-background 'cursor))
	     (set-frame-parameter nil 'my/repeat-cursor ccol))
	 (setq in-repeat nil)
	 (set-frame-parameter nil 'my/repeat-cursor nil))
       (set-cursor-color (if map rcol ccol))))
    (add-function
     :after after-focus-change-function
     (let ((sym 'my/remove-repeat-cursor-color-on-focus-change))
       (defalias sym
	 (lambda ()
	   (when in-repeat
	     (dolist (frame (frame-list))
	       (when-let ((col (frame-parameter frame 'my/repeat-cursor)))
		 (with-selected-frame frame
		   (set-cursor-color col)))))))
       sym)))

Updated to avoid using a post-command-hook (setting the repeat-echo-function instead), and handle the case of commands which change window focus.