Black and white. I’ve never thought about it, but you’re right. Just think of the tension in the scene on the bridge in the hurricane, Wow.
Don't get me wrong...I'm not a Luddite when it comes to color in film. Lawrence of Arabia with its breathtaking scenes (and sweeping music score) is a film that has to be in widescreen color. A black and white presentation would made it something other than the classic it's become.
There were some colorized versions of It's a Wonderful Life that have (hopefully) been destroyed. As uplifting as that story is, much of it is a dark film. The colorized versions turned it into fluffy, cotton candy piece.