Tome and Tone aren’t homophones, but they are easily confused words. They share all but one letter. The spell-check application in word-processing software doesn’t catch words that are spelled correctly, that are words, even if another word should have been used in that context.
Tome is a noun, meaning a book or one volume of a series of books.
Tone is a noun, meaning a type of sound. Music is full of tones. There’s a person’s tone of voice.
Interestingly, even writing, which has no actual sound, possesses a tone. Writing’s tone refers to the approach of the message’s delivery, the writer’s voice, the attitude of the writer about the subject matter and how that affects how you see the subject matter.
The following sentence uses both words correctly:
Thomas was disappointed that his tome didn’t sell, perhaps its subject or its tone didn’t resonate with readers.