To create such sharp visuals, director of photography Freddie Francis used lots of huge bright lamps. Deborah Kerr sometimes had to resort to wearing sunglasses between takes. He also had candles custom made with four or five wicks entwined to produce more light.
Truman Capote took a break from writing "In Cold Blood" in order to rewrite the screenplay for this film.
Producer and director Jack Clayton didn't want the children to be exposed to the darker themes of the story, so they never saw the screenplay in its entirety. The children were given their pages the day before they were to be filmed.
When Miss Giddens (Deborah Kerr) first arrives at the house, it's a bright, sunny day. In fact, Freddie Francis had had some of the trees painted lighter to exaggerate this.