I think that this sets a somber tone for the film. Color is added to show time progression. Then it's flashed back to when Cash was a young child and shows how his father was not proud of him. His brother was his father's favorite and this feeling is let known thought-out the film. When the father is around Cash, the demeanor of the two is distant and grudge-like. His brother dies after a wood cutting accident when the two were young.
The music is mostly Joaquin singing Cash's songs at particular points in the film. At certain points when Joaquin is listening to the radio, as a child, he listens to oldies music. It is sometimes so silent that the audience can get a feel of what the actors are feeling. This makes people feel that they are there in the scene themselves.
Panning shots are taken when Johnny and his band play their first gig, to show the emotions on all the band members' faces along with the crowd's reaction. A few close ups were taken when Johnny was in the recording studio. These were to make the audience focus on what he was feeling at that particular moment. Also, some were taken when Johnny and June start to fall in love. These conveyed a bittersweet tone to the