(eval-when-compile (require 'cl))
 (defun toggle-transparency ()
   (interactive)
   (if (/=
        (cadr (frame-parameter nil 'alpha))
        100)
       (set-frame-parameter nil 'alpha '(100 100))
     (set-frame-parameter nil 'alpha '(85 50))))
 (global-set-key (kbd "C-c t") 'toggle-transparency)