There are two types of color blindness. The most common is red-green color blindness, the less common form is blue color blindness. Both are cause by defective genes that control the production of rods in the retina. (Rods are the light sensors that allow us to see color.) In the case of red-green color blindness, the defective gene is found on the X chromosome and cause the red and green rod to respond to the same wavelengths of light. This gene is also recessive. Therefore, as long as the individual has a normal gene, they will not be color blind. Because of this, red-green color blindness is far more common among men than it is women. Since men only have one X chromosome, they have not backup if they inherit the defective gene. Since it is the x chromosome that carries this gene, the man inherits the condition from his mother and will bass the defective gene on to any daughters that he may father. However, he won't pass it on to any of his sons. In order for a woman to inherit this condition, she must get defective genes from both he mother and father. The gene for blue color blindness is also a recessive gene. However, it is not carried on one of the sex-linked chromosomes. Therefore, it is much less common because just about everyone is born with matched pairs of this chromosome. So, the only way for a person to develop this condition is to have two defective genes. Also because it is not on the sex-linked chromosomes, it is about as common in men as it is in women.