Incomplete dominance occurs when

the phenotype of the heterozygous genotype is an immediate of the phenotypes of the heterozygous genotypes.

Explanation:

Each of the alleles are partially expressed

Incomplete dominance (also called partial dominance, semi-dominance or intermediate inheritance) occurs when the phenotype of the heterozygous genotype is distinct from and often intermediate to the phenotypes of the homozygous genotypes. For example, the snapdragon flower color is homozygous for either red or white.