Final answer:
The son with color blindness inherited the gene from his mother, who is a carrier of the X-linked recessive trait. Since color blindness is carried on the X chromosome, affected males must inherit the gene from their mothers, as fathers contribute a Y chromosome that does not carry the allele for color blindness.
Step-by-step explanation:
The son inherited the gene for color blindness from his mother. Color blindness is an X-linked recessive trait, meaning that it is carried on the X chromosome and requires only one copy of the allele to manifest in males, who have one X and one Y chromosome (XY).
The father's contribution to the gene for color vision is always a Y chromosome, which does not carry the allele for color blindness. Therefore, a son cannot inherit color blindness directly from his father. However, a daughter may inherit a normal X chromosome from her father and a recessive allele from a carrier mother, becoming a carrier without expressing the trait.