The correct answer is D - the father must be colorblind.
Colorblindness is a recessive trait, so in order for it to appear, you would need either one heterozygous and one homozygous recessive parent, two heterozygous parents, or two homozygous recessive parents.
Males only have one X chromosome to give to make a female. Their other chromosome is a Y. These sex-linked traits only appear on the X chromosome.
Since colorblindness is recessive, this X chromosome the father gives must be recessive, meaning he must be colorblind.
The mother can either be homozygous recessive (colorblind) or a carrier.
