defvar-issue

(defvar hcz-set-cursor-color-color "")
(defvar hcz-set-cursor-color-buffer "")
(defun hcz-set-cursor-color-according-to-mode ()
  "change cursor color based on minor mode."
  (let ((color
     (if buffer-read-only "grey"
       (if overwrite-mode "red"
         "orange"))))
    (unless (and
         (string= color hcz-set-cursor-color-color)
         (string= (buffer-name) hcz-set-cursor-color-buffer))
      (set-cursor-color (setq hcz-set-cursor-color-color color))
      (setq hcz-set-cursor-color-buffer (buffer-name)))))
(add-hook 'post-command-hook 'hcz-set-cursor-color-according-to-mode)