Jack Burden's tone, as the narrator, is aesthetically beautiful and endlessly imaginative. Jack's narration is influenced by his unique worldview: he seems to find grand images and rich similes in almost anything.
At any moment in the novel, Jack's precocious memory and skill for flashback can throw the story into the past, or his endless arsenal of figurative comparisons can entirely morph a scene. This exuberant, energetic style of narration, independent from the events of the novel, suffuses the tone with wonder. Underneath all his other emotions in the novel, Jack's narration shows him to be endlessly and eagerly fascinated with the story of his life and those around him.
Jack is highly intelligent and sometimes smarmy, so his tone is often caustic and sarcastic. He enjoys "wit" and irony, so the narration is also often funny, usually darkly so. Jack is an earnest observer of the world around him and always presents himself as honest with the reader, creating a forthrightness and dignity in the tone as well—it appears as if Jack approaches the task of recording the story of Willie Stark with a sort of solemn intention, but along the way his personality and biases slip through. Jack is, in other words, a very believable narrator, whose tone reacts actively to the events of the story, but always reflects his witty, imaginative, assiduous personality.
Jack is rather obsessed with Willie, so his descriptions of him are always admiring. Jack thinks of Willie as something between a father and a brother, and while he occasionally has doubts, Jack remains devoted to Willie to the end. It would not be outlandish to assume that Jack feels an attraction to Willie similar to those felt by Anne, Sadie, and Lucy. All these characters understand Willie's flaws yet are inevitably attracted to him and prejudiced in his favor. This devotion certainly sweetens Jack's tone on the subject of Willie. It would be incorrect to say that the narrator always describes Willie positively; like the journalist he is, Jack honestly presents Willie's flaws and failures.
But even after Anne's affair with Willie and up to his death, Jack never loses faith in the Boss. So the tone, in regards to Willie, always has a sense of awe, fear, and love. Jack, who knew Willie better than perhaps anyone else, understood the depths of Willie's power, ambition, and righteous morality. Jack, in writing the story of Willie's rise and fall, describes the man with a tone of reverence, if not always respect.