Answer:
intermediate phenotype
Step-by-step explanation:
This question illustrates INCOMPLETE DOMINANCE, which is when two alleles of a gene are neither dominant over another, hence, they produce an intermediate phenotype that is a heterozygous for the gene in question. The intermediate phenotype is a blending of both parental phenotypes.
According to this question, Herman bred his black stallion (BB) with his white mare (WW) to produce foal/offspring that came out gray (BW). This portrays that the gray phenotype is an INTERMEDIATE PHENOTYPE of black and white in a kind of inheritance pattern called INCOMPLETE DOMINANCE.