In the opening scene, Marion Crane is wearing a white bra because Alfred Hitchcock wanted to show her as being “angelic”. After she has taken the money, the following scene has her in a black bra because now she has done something wrong and evil. Similarly, before she steals the money, she has a white purse; after she’s stolen the money, her purse is black.
“People say to me, ‘Now is she a bad guy or is she a good guy?’ good at heart but she was always running a stray, no pun intended… I thought it would be a couple of scenes, and probably y’know? not a fully developed character. But I didn’t care I would have done it anyway because it’s kind of idol from my childhood. then to my surprise I read the script, I found her to be very interesting, and very complicated sort of psychologically. And actually, quite a challenge as an actress.” - Michelle Pfeiffer