system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What makes primary colors "primary" (unable to be created by other colors), and why are we able to create secondary colors from primary colors?

Regarding primary colors, why is it that red, yellow, and blue specifically are the colors that are our base primary colors?  Also, I understand which primary colors create secondary colors, but how does that work?  Why do those specific color mixes create new colors?
gpt
Because our eyes actually cheat. They can't detect colors other than blue, red and green. What they do however is, using those three colors, your brain then can form very good guesses about what the color you see actually is. It's a very complicated process, but because your eye literally only has those 3 colors to form its guess from, you can cheat it with just the right combination of blue, red and yellow to make it arrive at erroneous conclusions about what it's actually seeing. Since real yellow activates both red and green sensors in our eyes, you can make brain conclude its seeing yellow simply by throwing both green and red light at the eye. The brain can't tell the difference between these cases since either way, eye is telling it that both red and green light sensitive sensors have activated.

It's important to notice there are actually two types of primary colors, based on how colors combine. Computer screen is additive. If you have red region, you can add green light to make the segment appear yellow. Paint on the other hand works by **substracting** light from what it receives. So if you mix yellow paint, which substracts blue and only lets out green and red, with magenta paint which substracts green and only lets out red and blue, resulting paint only lets out red color. So with substractive colors, primary colors are cyan, magenta and yellow. This is how printing works, for example.