Now this is going to be tricky. First of all, I am not a costume historian, I just like clothes and fashion history. And secondly, I’m going to try not to gush over Alfred Hitchcock, let me just say this now: I ADORE his movies.
So, not surprisingly, I’ve watched Vertigo (my favorite movie of all time) and The Man Who Knew Too Much (the newer version, and by that I mean the 1956 version with James Stewart) multiple times. It occurred to me during my latest viewing of The Man Who Knew Too Much, that Doris Day’s suit was awfully similar to Kim Novak’s in Vertigo.
Kim Novak in Vertigo as Judy as Madeline...
Doris Day in The Man Who Knew Too Much as Jo
I’m going to assume that this coincidence is no coincidence at all, and rather has everything to do with the fact that Alfred Hitchcock used the same costume designer in most of his movies: Edith Head. The Man Who Knew Too Much came first in 1956 and Vertigo soon followed in 1958, and both were costumed by Ms. Head …and starred James Stewart.
I found some references to these costumes on IMDB (Internet Movie Data Base). According to IMDB, “Edith Head and Alfred Hitchcock worked together to give Madeleine’s clothing an eerie appearance. Her trademark grey suit was chosen for its colour because they thought it seemed odd for a blonde woman to be wearing all grey.” But, they had already given this look to Doris Day, a blonde, two years earlier.
Jo McKenna at Ambrose Chapel in her gray suit and black hat
The one difference I notice straight away is the use of a hat. Doris Day’s character wears a black pill box hat with her gray suit and white mock turtleneck. Kim Novak’s character’s hairstyle actually plays an important role in the movie – as she is copying the style of a woman’s hair in a portrait. Kim Novak’s Madeline is also much more sensual and less proper than Doris Day’s Jo.
Doris Day with Alfred Hitchcock and Jimmy Stewart in the set of The Man Who Knew Too Much during her birthday
Kim Novak on the set of Vertigo with Alfred Hitchcock
So, the common denominator isn’t really Jimmy Stewart at all, but more likely, Edith Head. She was quoted as saying, “I don’t usually get into battles, but dressing Kim Novak for her role in Alfred Hitchcock’s “Vertigo” put to the test all my training in psychology.” I’m not sure if she’s talking about Kim Novak here or about how important the costumes were to the psychology of the movie and of the characters in the movie, I’d like to think the later.
Upstaged by Design 
The Man Who Knew Too Much (1957) is my favorite movie, only barely beating out Vertigo, and North By Northwest. The music has much to do with it, but costumes, photography, and acting are also big features here. Hitchcock is obviously the consumate craftsman, as well as a genius at telling a story, unwinding the details as you go, so we never lose interest.
I find myself wondering what hat James Stewart wore in The Man Who Knew Too Much. Everyone is wearing hats back then, and even my dad had a hat when I was a kid, not too much later. Stewart’s hat is grey, with a black grosgrain (I assume) ribbon. Not too wide a brim. I sure I can find the hat (I live near Hollywood and know the shops that outfit movies), but perhaps you know if it’s recorded somewhere.
I’m also a fan of Hitchcock’s movies. Doris does have different accessories but the suit also appears to be made of a different fabric. I also agree about the way it fit Doris. Always loved Days’ style but Novak looked sensational in the suit.
I am so glad you discover someone else who has noticed this similarity. In fact, I’d venture to guess that they are identical.