How do I make an Emacs-Lisp function available via M-x ?

[leonel.gayard@gmail.com]

Hi all,

I've recently started to add some Lisp functions to my .emacs file. For
instance, these two functions change the colors in Emacs, with white
fonts over black background or vice-versa:

;;;###autoload
(defun black-on-white()
    (and
         (set-foreground-color "black")
         (set-background-color "white")))

;;;###autoload
(defun white-on-black()
    (and
         (set-foreground-color "white")
         (set-background-color "black")))

Now, I would like to call these functions by typing M-x white-on-black,
but they simply are not available there. The apropos command (M-x
apropos) acknowledges that they exist, but when I type M-x
black-on-white, all I get is "no match".

Any ideas ?

[]'s
Leonel