I think it's because it was an emotional story, and emotions come through much stronger in black and white. Colour is distracting in a way, it pleases the eye but it doesn't necessarily reach the heart.

She attended Miami Beach High School. In 1959 Kim Hunter appeared in Rawhide season 1/16 episode Incident of the Misplaced Indians as Amelia Spaulding. Career
Hunter's first film role was in the 1943 film noir The Seventh Victim.

Decades later Kim Hunter received a Daytime Emmy Award for her work on the long-running soap The Edge of Night. She won both an Academy Award and a Golden Globe Award each as Best Supporting Actress for her performance as Stella Kowalski in the 1951 film A Streetcar Named Desire. Kim Hunter (November 12 1922 – September 11 2002) was an American film theatre and television actress.