Colour Blidness : It is a sex-linked recessive disorder due to defect in either red or green cone of eye resulting in failure to discriminate between red and green colour. This defect is due to mutation in certain genes present in the X chromosome. It occurs in about 8 per cent of males and only about 0.4 per cent of females. This is because the genes that lead to red-green colour blindness are on the X chromosome. Males have only one X chromosome and females have two.

A man whose father was colour blind (X^CY) has a zero per cent chance of being colour blind. a woman who had a colour blind mother (X^CX^C) and normal father (XY) is not herself colour blind because the gene is recessive. That means the man will be normal (XY) and women will  be carrier (X^CX). The cross between them is as:

Thus, 50% percentage of male children of this couple will be colour blind.