If black feathers are dominant over the grey feathers. A pure breed black feathers homozygous would have similar dominant alleles while the purebreed grey feathers homozygous will have similar recessive alleles. Therefore, a cross between a pure breed black feathers and a pure breed grey feathers results to heterozygous black feathers. All the offsprings will be black feathered and thus there is no possibility of getting a grey feathered penguin.
