It is common practice for actors to wear specific costumes on set, determined by the requirements of the film and the specific scene being filmed.  

Costume design plays a crucial role in creating the characters and visual atmosphere of a movie, and wardrobe choices are carefully selected to match the character’s personality and the storyline.

Jennifer Aniston’s decision to wear an all-white dress on the set of her new film likely fits the narrative and character she is portraying.