Your voice, as an author, is how you express your thoughts and put them down on paper. It reflects your personality, and it's what makes your writing different from everyone else's. It's often been said that there are, in writing, no new stories, and I tend to believe it. Last year my husband and I went to see the movie Avatar. About half way through the movie I leaned over and said, "This is just Dances with Wolves in space." The similarities were, to me, striking. But that doesn't mean the screenwriters stole someone else's idea--it just happens.
So how does a writer create something original? You do it by bringing your unique voice to the project, your way of seeing things and communicating your ideas to your readers. In my writing classes I sometimes give a prompt of 3 specific words, and ask the students to take ten minutes to write a story around those words. The results are always amazing. A group of twenty people will come up with twenty stories so different that the readings usually generate laughter and applause.
Two writers could be given a detailed plot for a book, told to write a story following the plot, and the end results would be so different from each other as to be nearly unrecognizable. That's because each writer brought his/her own unique vision to the story. In editing other writers' work, I'm always mindful of keeping that author's "voice."
Tone is the mood of your story. It can be lighthearted, whimsical, gloomy or just about anything in between. Tone also can, and should, vary within a book. The above-mentioned Dances with Wolves is a serious story about a soldier's lone journey to the untamed American West. Yet laced throughout are definite touches of humor. Same with Catch-22, Steel Magnolias, and yes, Gone with the Wind. If a story were relentlessly somber, the reader would be dragged down into despair and might even set the book aside before finishing it. The insertion of humor is a way to relieve the tension at regular intervals, and to prepare the reader for the next dramatic scene.
"I think I did pretty well, considering I started out with nothing but a bunch of blank paper." Steve Martin