Colourblindness is an #X# linked recessive disorder,so a for a female to be colourblind,both of her #X# chromosomes must be defective,and for a male to be colourblind his only #X# chromosome has to be defective.
Below I have worked out the pedigree analysis of the given case, where #X# indicates normal #X# chromosome and #X'# indicates chromosome responsible for colourblindness.
Now see the result,out of the #4# children, both the boys are colourblind as they received the defective #X'# chromosome from their mother.
whereas,the two girls,though they received one abnormal chromosome #X'# each,but the normal chromosome from father being dominant didn't make them colourblind,but both of them are carrier of the disease,that means when they will marry there will be chance that #50%# of their sons will be colourblind.
So,here in our case #%# of colourblind among all the children in #F_1# is #2/4 *100# i.e #50#
And, among males both are colourblind(#100%#) and out of the two females no one is colourblind (#0%#)