The rarest hair and eye color combination in humans.

Red hair with blue eyes is the rarest hair and eye color combination due to a genetic tweak that makes it unlikely to happen. The MC1R gene determines hair color, and only three of its variants are associated with red hair. The OCA2 gene controls eye color, and two nonfunctional copies of it yield blue eyes. Blue-eyed redheads are the absolute rarest, with only 0.17% of the population having that combination of hair and eye color.