Black Noir is black in the comics. The creators have designed the character in such a way to give a specific look and feel, and the black complexion is an integral part of that design.
Another aspect to consider is that it could be a way to develop his character further. Through his injuries and the pain he endures, we can see his growth, his vulnerability, and how he copes with difficult situations. This can add depth to his character in the fanfic.
The presence of black women in noir stories is important for cultural representation. It helps to break down the narrow view of who can be a part of the noir genre. They can also offer a different view on themes like justice, morality, and power dynamics, enriching the overall narrative of the noir story.