Final answer:
If human skin color were an X-linked trait, females could potentially display a mosaic of skin colors due to varying combinations of alleles and X-chromosome inactivation, leading to more diverse skin color expression than in males who would exhibit a single phenotype.
Step-by-step explanation:
If the genes for human skin color were located on the X chromosome, they would be considered sex-linked traits. Females have two X chromosomes, and the expression of X-linked traits depends on whether they are dominant or recessive. Had skin color been an X-linked trait, much like in the case of coat color in cats, females could exhibit a wider variety of skin color expressions due to the possible combinations of alleles.
Female humans could be heterozygous, carrying two different alleles one dominant and one recessive for skin color. Due to a process known as X-chromosome inactivation, which randomly turns off one of the X chromosomes in each cell, a female might express different skin colors mosaically across her body if one allele was for one skin color and the other allele for another. However, if skin color followed a simple dominant-recessive inheritance pattern and the dominant allele represented the common skin color, it would mask the effect of the recessive allele, leading to a uniform appearance.
For males, since they have only one X chromosome, the allele present there would determine their skin color outright, similar to how X-linked disorders express themselves more commonly in males than females. Thus, the variety of skin color presentation would be more limited to a single phenotype per male, as they cannot be carriers of a second, possibly contrasting, skin color allele.