The two alleles an individual has for a certain gene are identical. For genes on the X-chromosome like the L-opsin and M-opsin, males will have only one allele, but females have two. When those alleles are the same, the female is homozygous for that gene. If they are Homozygous Recessive, they will be colorblind. If they are Homozygous Dominant (the normal allele), they will be Color Normal.