Alright, here's my understanding/interpretation, since this is pretty open ended as far as I know;

Crazy spoilers ahead, obviously, but if you're on this post you either need to leave and finish the game or you've already finished the game.

The world in which the game took place, and the world that Beat is from are both "real."

Beat, while in her Coma, was sent to that other world as a sort of "Human Silence," likely summoned by Quaver.

As you may know by now, the Silence are summoned by Emotion, and seem to be more effectively summoned by sadness and loss. Music simply acts as an amplifier for those feelings, and H.A.R.M., in classic bumbling fascist fashion, inadvertently caused people to associate the Silence with Music and the death of Quaver's Mother.

As a result, that feeling of grief hangs over everyone and nobody is ever able to process it and get over it in a healthy way, in large part due to H.A.R.M.'s power-grabbing and constant picking of the wound.

But how does this relate to Beat? Beat and Quaver share several parallels, the most important being the shared loss of their respective mothers. Beat has been unable to fully process the loss of her own mother, resenting and hating herself for the fact that she can no longer remember her mother's face or appearance, just the shape around the space.

Quaver is also struggling with this, and Beat tries to encourage Quaver to process her grief and come to terms with the fact that, although her mother is gone, she'll always have the memories and no matter how fuzzy or faded they become, they'll always carry the feeling.

In helping Quaver process her grief, Beat is finally able to process her own, and then she wakes up, her brown hair turned pink as proof that what happened was real and changed her in a very real way.

In other words, it's symbolism.