Final answer:
The genotype for individuals with normal skin color is either AA (homozygous dominant) or Aa (heterozygous), which indicates at least one normal allele is present to be unaffected by alkaptonuria.
Step-by-step explanation:
The genotype for individuals with normal skin color can vary, however, based on the provided information, normal skin color is associated with individuals who do not have alkaptonuria, a recessive genetic disorder. Thus, to have normal skin color, at least one normal allele (A) must be present. Therefore, the possible genotypes for normal skin color could be AA (homozygous dominant) or Aa (heterozygous).
According to the passage, when neither parent has the disorder but their child does, both parents must be heterozygous, hence the genotype Aa. Furthermore, individuals on a pedigree showing an unaffected phenotype but an unknown genotype are designated as "A?" because they have at least one normal allele. This is consistent with Mendelian genetics, where uppercase letters represent dominant alleles, and uppercase represents recessive alleles.