Customisation for comment delimiter colour based on light or dark theme

[fatiparty]

I would like to adapt the customisation for comment delimiter colour to change 
according
to light or dark background.  How is this customarily done?

(defun annot ()
  "Customisation for comments"

  (set-face-attribute 'font-lock-comment-face nil
              :weight 'normal :slant 'italic)

  (set-face-attribute 'font-lock-comment-delimiter-face nil
              :foreground "#00FF00") )