A man whose father was colour blind marries a woman who had a colour blind mother and normal father. What percentage of male children of this couple will be colour blind?

Color blindness is an X-linked recessive disease. A man whose father was color blind (XcY) and mother was normal (XX; we will consider normal unless mentioned otherwise), is normal (XY; as he is getting a normal X from the mother and Y from the father). A woman who had a color blind mother (XcXc) and normal father (XY), will be a carrier (XcX; as she is getting one Xc from the mother and another X from the father). The offspring resulting from this couple (XcX and XY) are: XcX, XcY, XX, XY. Out of these four, two of them are males (XcY, XY) of which one is color blind (XcY). So, the chances of the male child being colorblind is 50%.