I was not aware the percentage was so high!
It's because of various misconceptions and various forms of colorblindness.
I got tested because people kept arguing with me. Being a rational person, I realized that I must be the problem. So, I went to get tested and to learn a bit more about my condition.
People tend to think that colorblindness is a total thing, that all they'll see are hues of gray. They might even realize that they don't quite see all the colors properly, but they can make do and it's never an issue for them. As it's not an issue, they never bother getting it checked.
It's not a crippling problem. Even if you're completely colorblind, you can still recognize the pattern of the lights at an intersection (for example). So, they just don't get diagnosed. They may self-diagnose, I suppose.
You can actually take a pretty solid colorblindness test online. I've found it for friends who were curious. I'll dig up a link...
This is just a quick test. The real test is much longer and much more difficult.
Take the #1 color blind test online to assess your vision in under 2 minutes. Discover your type of color blindness and explore EnChroma solutions today.
enchroma.com
I took the test (just tell it to bugger off and show you the results) and my results are here:
enchroma.com
As you can see, I'm not completely colorblind.
Also, the real test is much longer and the test has multiple types of tests within it.
DO NOT USE THE RESULTS AS ANYTHING CLINICAL!
It's just a website, not a doctor.