Although I have never heard of this before, synesthesia is a real condition. And although it's not always easy having synesthesia, when Mia temporarily loses this ability, she misses it and the world seems rather drab.
This is a wonderful book and quite short and easy to read. There are arguments with Mia's best friend, sorrow over the loss of her grandfather, and an unlikely romance with a boy Mia meets in an online support group. All-in-all, a lovely book and highly recommended.