Protagonist (detective) costume

What are the essential needs of a detectives costume and what to viewers expect to see the protagonist wear in the 40s?

The Three-Piece Suit

The classic grey three-piece suit was the most standard uniform of a detective in film noir which allowed him to look good and handsome but without attracting much attention to himself. The suit jacket is usually unbuttoned to show his vest/shirt underneath as well as leaving some room for his gun that would be hidden under his jacket.

The Fedora

A fedora with a thick black band was usually made to be worn with a suit and the goal was to seek minimalism with the outfit. The hat may be used to create mystery as it can be hiding the protagonist's face during some scenes or make some shots including shadows look extremely noir based.

The Trench Coat

Since a lot of rainy and damp weather is used in typical noir films, a trench coat is usually worn to create a meaning of foreshadowing dark, dangerous and mysterious situations.

The colour was always typically beige to contrast between the dark and the character and sometimes, the collar of the protagonist was turned up to hide his face, which again creates mystery.

All of these points regarding the costume of a detective is the iconic silhouette of the Film Noir detective.