What is the author's tone in the novel, Noughts & Crosses?

As the novel progresses, Callum and Sephy’s character development becomes reflected in their narration. Sephy, who was often petulant and self-pitying in her youth, grows into a more somber and reflective observer of the novel’s events. Callum, on the other hand, transforms from a hopeful, eager child to a disillusioned and remorseless man. This is reflected in the bitter tone he uses to recount events in the second half of the novel. These subtle shifts in the narrators’ tones mark the great changes in Callum and Sephy’s worldviews.