I am using the following function to change the colour of the comment delimiter.
Whilst the code works for a dark background, the colour is not changed when using a light background.
(defun delimkl ()
"Set comment delimiter colour."
(if (eq 'dark (frame-parameter nil 'background-mode))
(set-face-attribute 'font-lock-comment-delimiter-face nil
:foreground "#00FF00")
(set-face-attribute 'font-lock-comment-delimiter-face nil
:foreground "#004700") ))