Color blindness is due to a defective gen that express one of the three kind of cones in the eye. Usually the cones more sensitive to middle length photons (M ~green) become closer to the cones more sensitive to long length photos (L ~red) and thus they can only discriminate colors in between thanks to the other short length cone (S ~blue), but the S cones are almost blind to these colors.
The thing is, these genes are in XY chromosome in males, and thus we only have a single copy for each of these genes. Women have two copies of each gene, so even if one goes wrong, the remaining one can express the cones.
Funny thing is woman with a defective gen usually just goes unnoticed, but the defective gen in some cases can express a fourth kind of cone with a peak sensitivity between M and L cones, allowing them to perceive colors that usual humans can't perceive.
The thing is, these genes are in XY chromosome in males, and thus we only have a single copy for each of these genes. Women have two copies of each gene, so even if one goes wrong, the remaining one can express the cones.
Funny thing is woman with a defective gen usually just goes unnoticed, but the defective gen in some cases can express a fourth kind of cone with a peak sensitivity between M and L cones, allowing them to perceive colors that usual humans can't perceive.