When ghosts appear, even imaginary ones, they don't always raise the fright meter. I thought that they were interesting spirits, with a message that new RKO studio boss, Howard Hughes didn't like. Imagine the adult, Howard Robard Hughes browbeating 12-year-old Dean Stockwell to say pro-War lines! Now THAT is frightening.;)

Considering the movie was in black and white just to begin with thus it was extra-scary just to start. Especially the poster boy who really stared deep. I do not know what on Earth you mean about Hughes browbeating.

Black and white film is almost automatically considered terrifying. It was way easier for original TZ to scare than Night Gallery!

"The Boy With Green Hair" Movie trivia: https://www.imdb.com/title/tt0040185/trivia I also saw this movie in black-and-white, long before we got a color TV. (Or was the black-and-white print the only one that was available to the TV station back then?) Turner Classic Movies showed this Technicolor (sorta) Musical last week, which was a visual revelation to me. You said: "Black-and-white film is almost automatically considered terrifying." It is? Check out "Our Vines Grow Tender Grapes," a 1945 rural tale that featured Edward G. Robinson in a non-gangster role. https://www.imdb.com/title/tt0037963/reference It is about as scary as the Sepia-tinted before and after scenes in "The Wizard of Oz." As for Rod Serling-era "The Twilight Zone," that was great screenwriting translated to film by talented actors and directors.

Google "Why are movies scarier in black and white".