As is often the case in literature, darkness (blackness) symbolizes evil and the mystery of the unknown, while the daylight world is a place of relative safety and innocence. Nearly every bad thing that happens during the course of the novel occurs at night: the children's dangerous raid on the Radleys' back porch; Miss Maudie's house fire; the lynch mob at the jail; and the climax of the story when Bob Ewell attacks the children on their way home from the Halloween pageant. Boo Radley prowls only at night, and the darkness also provides a cover for most of Bob's evil activities. The children have no worries during the day, when they attend school, act out the Radley game, and play with a full run of the neighborhood.
Our nightmare had gone with the daylight... (Chapter 17)
Black and white is also symbolized by the races: Negroes are considered inferior and untrustworthy,
"... the evil assumption--that all Negroes lie, that all Negroes are basically immoral beings...
"a lie as black as Tom Robinson's skin..." (Chapter 20)
The "morphodite snowman"--black on the outside and white on the inside--transforms following the house fire, turning black and suggesting that "skin color is a limited distinction that reveals little about an individual's true worth." The Ewells cannot erase their own evil appearances even by a good scrubbing. Burris Ewell comes to school with blackened skin, "the filthiest human I had ever seen." Bob attempts to clean himself up before his appearance at the trial, but
All the little man on the witness stand had that made him any better than his nearest neighbors was, that if scrubbed in lye soap with very hot water, his skin was white. (Chapter 17)
In the final scene, as Atticus reads to Scout while watching over the injured Jem, Scout is secure in her father's lap with the light on. When Atticus "turned out the light," a long, anxious night awaited him, but all would be well "when Jem waked up in the morning."