Continuity mistake: When Young Barry slouches on the chair to eat peanut butter, the way the left side of his robe falls on the chair differs between shots.
Continuity mistake: After Young Barry vanishes, Old Barry holds the robe from the upper part. When Young shows up, Old's hand is nowhere to be seen; the grip has changed.
Continuity mistake: When Young Barry vanishes in the kitchen, the way his empty robe folds changes between shots. Also, the spoon falls on the robe but suddenly appears on the floor a shot later.
Continuity mistake: Barry spits the broccoli and some gets stuck on his lower lip. A shot later it has vanished.
Continuity mistake: Young Barry forces Old Barry into eating broccoli, which he does in large bites. When Young retrieves the broccoli, it's uneaten.
Continuity mistake: When Young Barry enters Old Barry's home, he puts on a robe with a teddy-bear hood. The way the left side of the hood is folded changes between shots.
Continuity mistake: When Bruce is explaining about time travel issues to the Barries, the amount of sauce on the spaghetti changes between shots. The spaghetti in the bowl shifts as well, most noticeably when there's some right up on the lip of the bowl close to Bruce, which then disappears from another angle.
Answer: Some possible reasons gleaned from the Internet: Filmmakers wanted a different vision of Supergirl to reflect a darker, grittier personality and to show her refugee-like experience. Her dark short hair symbolizes her harsher journey from her home world. Also, it gives her a more androgynous look, reflecting both her feminine and masculine traits. Adopting a radically different look for an established character also shakes up viewers' expectations and generates more publicity and interest in the film.
raywest ★