A colour blind man marries a woman with normal sight who has no history of colour blindness in her family. What is the probability of their grandson being colour blind?

Colour blindness is X-linked recessive ($X^c$).Man ($X^{c}Y$) $\times$ Woman ($XX$).All daughters are carriers ($X^{c}X$), all sons are normal ($XY$).A carrier daughter ($X^{c}X$) marries a normal man ($XY$).Their children: $XX$ (Normal female), $X^{c}X$ (Carrier female), $XY$ (Normal male), $X^{c}Y$ (Colour blind male).Among the grandsons (sons of the daughter), the probability is $0.5$ (or $50\%$).