Let’s call them allele A, allele B and allele C. A diploid organism always has 2 alleles, which can be equal or different. So you can figure out these posible combinations: AA, AB, AC, BB, BC, CC (please note that AB = BA, so that counts as 1 genotype; the same with AC = CA, BC = CB). So there are 6 different posible genotypes. Besides, this doesn’t mean there are 6 phenotypes – you will have to gather information about dominance to see which phenotype is produced by each genotype (there are usually less phenotypes than genotypes).