The gene for red hair is recessive to the gene for black hair. What will be the hair colour of a person if he inherits a gene for red hair from his mother and a gene for black hair from his father?

The hair colour of a person will be black because the black hair gene is dominant over the red hair gene.

Also, it will be regardless of which parent passes a dominant or recessive gene. Dominant gene will express themselves in all the cases and the recessive gene can only express themselves in the absence of a dominant gene.