Answer:
Incomplete Dominance
Explanation:
When two organisms that are true-breeding for different colors are bred, their offspring will show incomplete dominance. This will result in the offspring having all grey feathers. In the attached punnet square, a true-breeding red flower (R) and a true-breeding yellow flower (R') are bred to produce 4 orange offspring (RR').
Codominance makes offspring display both phenotypes separately. So, the chicken babies would have white and black feathers, no grey.
Complete dominance would be if one allele dominated the others. For example, if all of the whitexblack chicken babies were black
Simple dominance is when a gene is controlled by only two alleles, one dominant and one recessive, and shows complete dominance.