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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. But why?

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.

My mother's father was colorblind. He was XY had one defective x-chromosome, which he passed to my mother. But my mother is XX. Her x, which she got from her mother, works fine. So she isn't colorblind. But she is a carrier.

That means that when she has a child, she has a 50% chance of passing that defective x-chromosome along.

My father (XY) passed me a y-chromosome. And my mother passed me her defective x. That means my only x is defective, so I'm colorblind. If they had an XX child tomorrow, that child would have a 50% chance of becoming a carrier like my mother. If my father were colorblind as well (he isn't), that two-x-chromosome child would have a 50% chance of being born colorblind, and would definitely be a carrier.  

All of which is to say: It's much easier for an XY person to be colorblind, and most XY people are male. That's why men are much more likely to be colorblind.

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