It’s very touching, and the two scenes give the audience a certain sense of satisfying symmetry. Yet today, when almost everything on screen is judged by how realistic it looks, it’s hard to ignore that the sunset looked… Why is that?
However, according to the DVD commentary for “The Outsiders – The Complete Novel”, this sunset was not real. Rather, it was a slowed-down shot of a sunset projected onto a screen at the Tulsa State Fairgrounds while Howell and Macchio played in front of it (via Tulsa World).
All in all, the scene still works, if only because the pink and gold tones are so vibrant they almost seem overdone. After filming wrapped, distributor Warner Bros. demanded a large number of cuts from Coppola, shortening the film from more than two hours to an hour and a half (via The Guardian). Although The Sunsets made it into the first theatrical release, Coppola later felt that far too much had been cut. That was one reason he released The Complete Novel on DVD in 2021.
https://www.looper.com/1024032/why-the-outsiders-sunset-scene-looks-so-funky/ Why the Outsiders sunset scene looks so crazy