the first advice I can give is not to use aquamacs. Gnu emacs for macos is much better and much more powerful and complete. You can find it here -> http://emacsformacosx.com/

from there on you need to make sure smalltalk mode is enabled when an st file is opened to see syntax highlighting.

From: Oscar E A Calla� <oalvarez@dcc.uchile.cl>
To: "Pharo-project@lists.gforge.inria.fr" <Pharo-project@lists.gforge.inria.fr>
Sent: Monday, 8 October 2012, 17:51
Subject: [Pharo-project] Emacs and Smalltalk code

Hi all,

I'm using Aquamacs (mac UI for emacs) as my default editor. But I have a problem, when trying to read a .st file, I don't get the syntax highlighting (so all is black-&-white). How I can solve this issue?

Cheers.