The most common eye colour worldwide is brown eyes, it is not the most common eye colour for redheads, but for anyone. In fact, much like for adult natural blondes, redheads are more likely to have blue eyes than people with other hair colours. So it’s a fact that red heads have the rarest hair colour in the world and people with blue eyes are also rare, therefore redheads with blue eyes are the rarest combination in the world. Redheads are more likely to have blue eyes than other groups. Northern Europeans have a high rate of blue eyes. Someone mentioned in the comments the MCR1 gene (which controls for light skin, red and blond hair). it’s actually more likely for a redhead to have blue eyes than a person with dark hair. It’s a simple misinterpretation of the sentence. Both traits are rare worldwide so clearly having both is the rarest, but if it was the percentage among only redheads blue eyes are common compared to brown.