Nick's tone does indicate to the reader Nick's attitude toward Tom in The Great Gatsby, since the definition of tone is the speaker's attitude toward the subject. Nick describes Tom numerous times, but I'll center on description in one incident, in the final chapter of the novel when Nick happens to meet Tom on the sidewalk:
One afternoon late in October I saw Tom Buchanan. He was walking ahead of me along Fifth Avenue in his alert, aggressive way, his hand out a little from his body as if to fight off interference, his head moving sharply here and there, adapting itself to his restless eyes. Just as I slowed up to avoid overtaking him he stopped and began frowning into the windows of a jewelry store.
And again after they talk and Tom tries to rationalize why he told Wilson that Gatsby owned the car that hit Myrtle, and after Tom indirectly reveals that he still doesn't know that Daisy was driving the car:
I shook hands with him; it seemed silly not to, for I felt suddenly as though I were talking to a child.
The tone in this description is Nick's attitude toward his subject, Tom. It is not necessarily the diction he uses or the content of what he reveals. Presumably, the speaker reveals what he sees. Though any speaker interprets as he describes--Tom's walk is aggressive, for instance--the tone, specifically, refers to only his attitude toward his subject.
Therefore, Nick's tone here is, I suggest, one of skepticism.
And skepticism reveals that Nick expects Tom to exhibit negative character traits. Nick's attitude toward Tom is that Tom isn't much of a human being.
The character traits from the above passages reveal what Tom is like as seen through Nick's eyes: aggressive, self-centered, haughty, restless, etc. But that is the characterization revealed in the passages. Tone is Nick's attitude toward Tom, and I suggest the tone is skeptical.
Nick Carraway really does not like Tom Buchanan much. You can see that in the tone of his description of Tom in Chapter 1.
In this description, everything about Tom is described in very violent, aggressive words. Nick's tone is of someone who is perhaps a bit intimidated and pretty turned off in general. Let's look at some of the words he uses to describe Tom:
- Enormous (again)
All of these words, are really quite aggressive, and give us a definite impression that Tom is a somewhat violent man.