Different settings

The setting in film noir films are usually urban scenes, such as apartment blocks or back alleys. These urban settings are usually filled with dark corners, shadows and little lighting, which shows the audience that there could be more than what meets the eye.

Although in some film noir films, it doesn't have to be the stereotypical dark alleys, black and white effects, etc. As long as there is a protagonist, a version of a femme fatale and possibly an antagonist.

Many people immediately think of black and white films when somebody mentions film noir but there are still a lot of film noir films produced nowadays that don't have any hint of black and white or the typical old movie feel. For example, https://www.fandango.com/movie-news/11-modern-film-noir-movies-you-must-see-748489

This link gives a list of many modern day film noir films such as 'Kiss Kiss, Bang Bang', 'Gone Baby Gone', 'The Dark Knight', and 'Drive'.

All of these films have some sort of protagonist, femme fatale and antagonist.

In this screenshot of The Joker (Heath Ledger) in 'The Dark Knight', we can immediately tell that he is the antagonist in the film due to his makeup and choice of clothing. Also the evil facial expression that he pulls at Batman who is the protagonist of the film. In film noir, the audience should be told immediately who each of the characters are and what they represent so they understand the meaning of the film more.