Yeah, it comes up in Les Mis fandom because several characters have hair that is colored French "chatain" and no translators, much less fans or casting directors, can agree on whether they are blonde or brunette! I would say "brunette" is anything from deep raven black to a medium chestnut, but I have seen people argue both that medium chestnut is too light for brunette, and that "brunette" goes all the way up to what I'd call "sandy" or "dirty blond" (and also argue over what medium chestnut and sandy and dirty blond are!). So basically the conclusion of my corner of fandom is that English just needs to adopt "chatain" for "neither dark nor light" like 19th century French.