Final answer:
The likelihood that this couple's first son will be color-blind is 50%. Color blindness is an X-linked recessive trait.
Step-by-step explanation:
According to the information provided, the son of a woman who carries the colorblindness trait and a male with normal vision has a 50% chance of being colorblind. Color blindness is an X-linked recessive trait, which means that mothers pass the recessive allele for the trait to their sons, who can then pass it to their daughters.