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 ?

A colour-blind man (XcY) marries a woman with normal sight (XX) who has no history of colour blindness in her family. Their offspring: Carrier daughters: XCXc ,  XCXc Normal sons:  XY,  XYAssuming that the carrier daughter (XCXc)is married to a man with normal sight (XY), the possibility of their son being colour blind is 25% or 0.25.(Question should be more specific)