Colorblindness is a fairly common condition where a person’s eyes conflate certain colors or don’t see colors at all.
It’s also way more common in men than in women.
The most commons forms of colorblindness are genetic conditions, passed along the x-chromosome. People with an x-chromosome and a y-chromosome only need their one x to be defective to catch it. People with two x-chromosomes need both to be defective.
Most women have two x-chromosomes (XX), and most men have an x-chromosome and a y-chromosome (XY). That’s why colorblindness is much more common in men than in women.