X-linked recessive disorders require two affected (recessive) alleles Xb to express in the female, but requires (the) only one in the male.
Therefore there are no male carriers. Â A normal male has the XB allele, and the affected male has the Xb allele.
A female either has 2 XB alleles, in which case she is normal and not a carrier.
If she has XBXb alleles, then she is a carrier, but phenotype is normal.
If she has XbXb alleles, she will exhibit colour-blindness.
Since woman's father has colour-blindness and she has normal vision, she is a carrier, because she has XBXb alleles.
Her husband has normal vision, so he has (one) XB allele.
Here's the Punnett square
Mother      XB (father)
XB Â Â Â Â Â Â Â Â XBXB Â (normal vision)
Xb         XBXb  (carrier)
We see that the XbXb (colour-blindness) case is missing, so the phenotype colour-blind is not expected (unless other medical conditions are present)
