Override comment face in one mode only

[Sebastien Vauban]

Hello,

I [1] would like to override the global green colored comment face just for
LaTeX buffers.

I tried to come up with the following:

--8<---------------cut here---------------start------------->8---
(add-hook 'latex-mode-hook
          (lambda ()
            (set-face-attribute 'font-lock-comment-face nil
                                :weight 'bold
                                :foreground "gray")))
--8<---------------cut here---------------end--------------->8---

but the comments are still green...

And, is it possible to have a local definition of a face?  Or would gray
become the color for all buffers (LaTeX and others)?

Best regards,
  Seb

[1] A friend of mine, in fact...

-- 
Sebastien Vauban