In incomplete dominance, the resulting phenotype of the offspring is a blend of the two parental phenotypes. When a black chicken (BB) is crossed with a white chicken (WW), the offspring will have a phenotype that is intermediate between black and white.
Given your options:
- All white
- All gray
- All red
- All black
Since the blending in this case would result in gray chickens, the expected phenotype of the offspring would be All gray.