PASSING: I was multitasking when the film was on, so I won't provide an analysis of the structure. I'll need to rewatch for that.
What I will say as someone who has not read the book is that this film didn't seem like a story about passing. The majority of the scenes were either in light mixed company or majority-black company, which doesn't provide insight on the passing experience - the benefits or setbacks because of it. We truly only saw both women passing in one scene at the very top of the film.
In my opinion, this was a closeted-lesbian love story or an infatuation or jealous frenemy story told under the guise of a story about passing for shock value. Had neither of these girls been passing or even light-skinned, a lot of the film would've read exactly the same. Those who didn't know/understand much about passing before the film won't have learned a thing.
Lastly, the casting of two women who could never actually pass undermined the entire concept and weakened the impact of the film. Of course, they were great actors, but this was a moment where casting for skin color was necessary.