According to Wikipedia:
Urban fiction , also known as street lit or street fiction is a literary genre set in a city landscape; however, the genre is as much defined by the socio-economic realities and culture of its characters as the urban setting. The tone for urban fiction is usually dark, focusing on the underside of city living. Profanity, sex, and violence are usually explicit, with the writer not shying away from or watering-down the material. Most authors of this genre draw upon their past experiences to depict their storylines.
So you don’t need black MCs as far as I know - I think a lot of Urban Fiction just happens to have black MCs.
I also checked out Goodreads and they have the word for word same definition of the genre.