The problem is that our templates in CakePHP end with *.thtml and so the Aptana Plugin doesn’t recognise it as HTML code and doesn’t hightlight it. The solution is to associate the ending to the right Editor.
In Eclipse go to “Window” -> “Preferences”
In this dialog choose “General” -> “Editors” -> “File Association”
Now you can add the new Assoication to *.thtml to Aptana HTML Editor.