As I had written elsewhere, my apostrophes come in light blue, which makes them even less noticeable than usual, which kinda defeats the point, I think? :)
Topic on Extension talk:CodeMirror
You can change the color/styling for yourself (in your common or global.css) using the class names at m:Community Tech/Wikitext editor syntax highlighting#Color and style customization.
However, I personally agree it might be beneficial to add font-weight: bold
to that particular class, or something similar.
Thanks for posting this -- I'm going to collect all the feedback on colors, and we'll figure out changes that we want to make.