highlight-regexp asks for a face to highlight the matches. If it's a complicated file structure when one wants to apply multiple faces to demote, emphasise, etc. parts for readability, then the face selection could be much easier if beside listing the names they also had their properties (color,etc.) applied to them, so the user could see instantly which faces are suitable to apply to various parts of the file.
Like read-color shows the color names with their actual colors, the selection of a face should also show the names with their properties applied.