Based on this information, what is Digby's phenotype for the fur color trait?

 - brown fur
 - black fur
Digby's genotype for the fur color gene is ff. Digby's genotype of ff has only f alleles. The f allele is for brown fur. So, Digby's phenotype for the fur color trait must be brown fur.
To check this answer, consider whether Digby's alleles are dominant or recessive. The allele for brown fur (f) is recessive to the allele for black fur (F). This means F is a dominant allele, and f is a recessive allele.
Digby's genotype of ff has only recessive alleles. An organism with only recessive alleles for a gene will have the recessive allele's version of the trait. So, Digby's phenotype for the fur color trait must be brown fur.