In The Lodger and Blackmail, Hitchcock begins his use of blonde women in his movies. He uses particularly blonde women because the light hair and fair skin symbolize purity and innocence. However, because Hitchcock is Hitchcock, he twists the women characters and shows a darker side that juxtaposes their innocent look. This is in an effort to show the audience how even the most innocent person is capable of doing dark, unpredictable things.
Daisy is the “Hitchcock blonde” in The Lodger. Daisy is immediately drawn towards the mysterious Lodger. For much of the film, the Lodger is presumed to be the killer, so for Daisy to fall for him shows that Daisy has an inclination towards the dark and dangerous.
Also, the killer in The Lodger is killing specifically blonde women which again associates blonde women with evil and darkness.
Alice is the “Hitchcock blonde” in Blackmail. Alice murders a man in self-defense, and is then haunted by guilt. This again shows how even though she maintains an innocent and pure outward look, she holds an inner darkness.