Conditional formatting has always been a pain point in Share Point 2013 and Share Point Online (Office 365).
It allows you to style your list, apply color schemes, manage font-styles and colors - all on top of you regular Share Point user interface.
So to create this note field we can add a field similar to the following: Note: Share Point uses the suffix _0 appended to the display name of the field and Tax HTField0 after the static name so I’m following those conventions.
To link the two together we can update the field we created in step one to include a customization section that points to the note field as shown below: Note the value within the Text Field property is the ID of the note field we created above.
When we add either the site column or content type to a list the managed metadata field works and shows up in the search refinement panel (at least it did in my testing).
This is due to the fact that Share Point automatically wires some extra bits (shown below) when the field is added.