Why are X-linked recessive traits such as red-green color blindness more common in males?

X-linked recessive traits, such as red-green colour blindness, are more common in males because of the fundamental differences in sex chromosomes between males and females.12

In humans, females typically have two X chromosomes (XX), while males have one X and one Y chromosome. Because the X chromosome is much larger and carries significantly more genes than the Y chromosome, the two do not form a truly homologous pair.123

When a male inherits a recessive allele for a trait on his single X chromosome, he has no corresponding allele on his Y chromosome to counteract or suppress its effects. Consequently, the recessive trait is expressed as if it were dominant. In contrast, a female must inherit the recessive allele on both of her X chromosomes to fully display the trait. If she inherits the allele on only one X chromosome, she typically remains a carrier with normal vision, as the second X chromosome provides a functional copy of the gene.1324