So, as an experiment, I created a simple wiki page for eyebrows behind hair and started tagging posts with it. I went through the images uploaded on the past day with -eyebrow_visible_through_hair and, although I surely missed some, I found only about 30 of them, hidden within a multitude of untagged eyebrows visible through hair. This confirmed my suspicions that
1) The subversion of the transparent hair trope is much rarer than the trope itself; and
2) Tagging its absence would be much easier, it would only need to become well-known.