Overriding emacs org-mode faces
<p>I am trying to override the default syntax highlighting in <code>org-mode</code> and <code>org-agenda-mode</code> buffers.</p>

<p>To clarify my intention: my current reason for doing this is to highlight headings (or parts of headings) based on their tags. The built-in variable <code>org-tag-faces</code> only allows customisation of the tag itself, not the heading containing the tag.</p>

<p>With reference to the following related questions:</p>

<ol>
<li><p><a href="https://stackoverflow.com/questions/6258455/emacs-font-lock-mode-provide-a-custom-color-instead-of-a-face">Emacs font lock mode: provide a custom color instead of a face</a></p></li>
<li><p><a href="https://emacs.stackexchange.com/questions/8211/color-code-a-new-generic-character-combination">https://emacs.stackexchange.com/questions/8211/color-code-a-new-generic-character-combination</a></p></li>
<li><p><a href="https://emacs.stackexchange.com/questions/8222/how-to-make-the-custom-font-lock-keywords-not-override-the-default-major-mode-fo#comment12615_8222">https://emacs.stackexchange.com/questions/8222/how-to-make-the-custom-font-lock-keywords-not-override-the-default-major-mode-fo#comment12615_8222</a></p></li>
</ol>

<p>In thread 2 the accepted answer is to use font-lock for this purpose.</p>

<p>In thread 3 I am trying to achieve the exact opposite of the poster. The last comment by <a href="https://emacs.stackexchange.com/users/160/jordon-biondo">Jordon Biondo</a> says:</p>

<blockquote>
  <p>take out the t from your keywords, what that t specifies is that font-lock should override already colored things. </p>
</blockquote>

<p>Since I want to override already coloured things I am adding in the t but as far as I can tell the <code>org-mode</code> highlighting is still overriding my custom face.
In <code>org-mode</code> buffers this manifests as the main body of the heading text being changed but any other items such as todo-states, dates, tags etc. retaining there existing faces.
In <code>org-agenda-mode</code> buffers it completely fails to modify any aspect of the matched lines.</p>

<p>By way of a simple example here is some code I'm trying to use to set any lines containing :TT: to red in <code>org-mode</code> buffers:</p>

<pre><code>(add-hook 'org-mode-hook
                (lambda ()
                  (font-lock-add-keywords
                   'org-mode
                   '(
                     ("^.*:TT:.*$" 0 '(:foreground "#FF0000") t)
                   ))))
</code></pre>