In chickens, the allele for black feathers is co-dominant with the allele for white feathers. Black-feathered and white-feathered birds are for either the black (B) allele or the white (W) allele.

a. heterozygotes
b. homozygotes

Explanation:

Co-dominance is a gene interaction in which both alleles of a gene are equally dominant and express themselves equally.

Since the  genes for black feathers and genes for white feathers are co-dominant,presence of both the allele in the organism (heterozygote) will result in speckeled phenotype.

So the birds with complete black feather or complete white feathers will be homozygotes for the respective alleles.