I think that the point is about whether a B&W movie would be shot on B&W film or colour film. Recent movies have shown that a good-looking B&W film can be made from a colour camera neg, which may then be printed on colour print stock. There is a much wider range of colour motion picture film available than B&W, especially after Ilford completely pulled out of motion picture film and abandoned the B&W market to Eastman Kodak. EK still make two B&W MP neg films, bless 'em.

Best,
Helen