1212A gene for eye color in humans has 3 alleles: , , for brown, blue, and green eyes, respectively. If an individual is , is she homozygous or heterozygous for eye color?

Alleles are pairs of genes on a chromosome that determine hereditary characteristics, such as eye color. You inherit one allele for each gene from each of your parents (this is the same with all organisms that reproduce via sexual reproduction).
In some cases, both parents provide the same allele of a given gene, and the offspring is referred to as homozygous (“homo” meaning “same”) for that allele. In other cases, each parent provides a different allele of a given gene, and the offspring is referred to as heterozygous (“hetero” meaning “different”) for that allele.
Since the individual in the problem has two different alleles, she is heterozygous.