The traditional witch’s hat commonly associated with Halloween is black.
Its familiar design is a tall, pointed crown with a wide brim. The exact origin of this image is disputed: theories connect it with the medieval Judenhut, the Phrygian cap, anti-Quaker imagery, and the hats supposedly worn by women who brewed ale for sale. None establishes one universally accepted source.
Black became a powerful visual shorthand for witchcraft because European and later popular culture often linked darkness with magic, secrecy, evil, and the supernatural. The image was reinforced by books, illustrations, stage productions, films, and Halloween decorations. L. Frank Baum’s 1900 novel The Wonderful Wizard of Oz and its 1939 film adaptation helped cement the pointed witch-hat silhouette in modern culture.
Green, orange, and purple are popular Halloween colors and may decorate modern hats, but they are variations rather than the standard traditional color. A black pointed hat is therefore the canonical quiz answer.