See, details matter in La La Land. The fact that Mia changes out of heels to matching tap shoes when Sebastian and her have their twilight dance is important; we won’t see her in heels again until she’s left Sebastian. That Sebastian drives a classic, brown Riviera distinguishes him from Mia’s sensible, modern Prius.
Likewise, the color pallette of a scene matters. Director and writer Damien Chazelle’s bright, detergent-commercial colors are (like many mechanics of the movie) an homage to big Hollywood musicals of old. But the primary color choices he makes also conveys much more about the pair of artists, and the lives they choose to lead.