You can use special modes like django-mode or MuMaMo .
If you want something very simple and assuming you are editing in html-mode, you can try the following:
(defun django-highlight-comments ()
(interactive "p")
(highlight-regexp "{%.*?%}" 'hi-orange))
(add-hook 'html-mode-hook 'django-highlight-comments)
(Just add the above lines to your .emacsor init.el, and eval it or restart emacs).