Why was To Kill a Mockingbird shot in black and white?

Answer 1

If you're referring to the television series "The Rifleman", most television series made prior to 1965 were filmed in black & white. It cost more to film in color and color televisions took a while to become mainstream. Some series such as Gunsmoke and Gilligan's Island started before 1965 and ended after. So the early episodes were black and white and the later ones were in color.

Answer 2

Black-and-white films were still common in 1962, when the Gregory Peck film was released.

As late as the 1960s, many films were shot in black and white because it was cheaper to film, stage, and distribute. Since the 1970s, black and white film is still used for budget reasons (student films, independent films) and in rare cases where a famous filmmaker is using the medium for aesthetic reasons.