Why is the son who recieves the allele for colorblindness from his mother always colorblind?

Beacuse men only have one X chromosome so beacuse colourblindness is found on the X chromosome then if the X inherited from his mother contains the allele for colourblind then he will be colourblind. women have two X chromosomes so even if they inherit one colourblind allele then if the other X contains a normal vision allele then they will be able to see normally.