The gene responsible for red hair is recessive, meaning a person needs to inherit two copies of the gene (one from each parent) to express the trait. While the red hair gene (MC1R) is present in all populations, it is less common in people of African descent.
Therefore, if two black people who both carry the recessive gene for red hair have a child, that child could be born with red hair. The hair might also be a lighter shade of brown with reddish undertones.