gnus-user-format-function, gnus-replace-in-string, color

[Dan Jacobson]

I want to make a summary line or parts of it jump out with color if
gnus-user-format-function-n finds an "N", but apparently %{, %}
etc. are evaluated too early for that.

(setq gnus-summary-line-format
      "%U%R%z%I%(%t|%~(cut-left 3)d%~(max-right 2)d%4L|%-20,20f%)%un:%s\n")
(defun gnus-user-format-function-n (header) ;Steib
  (let ((case-fold-search t)
        (val (or (cdr (assq 'X-NOFFLE-Status (mail-header-extra header)))"")))
   ;first letter of each X-NOFFLE-Status item
    (gnus-replace-in-string val "\\([A-Z_]\\)[A-Z_]* ?" "\\1")))
;How to change the color of the Summary line or parts if we find an "N"?

In fact, I don't even know how to just add a further
(gnus-replace-in-string val "N" "**N**")
without overriding the first gnus-replace-in-string, which is a non
documented function I was told to use.