system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How did we figure out we can only see 3 different colors with our eyes?

 I imagine there was a gradual process of discovery and little by little we learned more about the way we process light and send it to our brains. But I'm still having a really hard time understanding how we even started to question how many colors we see in the first place. Would really appreciate an explanation.
gpt
First we discovered that we have two different types of light receptors, rods and cones, by dissecting retinas and examining them under the microscope.

we were able to figure out that rods were responsible for low light, black and white sharp details and cones responsible for color vision by analyzing which parts of the eye are more sensitive to different types of vision, and comparing them to wear cones and rods are most dominant.

And after that, to answer your question, we found out that we have three different primary colors that we see because we we're studying rods and compare chemistry and we realized they have three different chemical receptors in them, each of which response to a different frequency range of light.

there actually are a very rare number of people that have four rather than three different photoreceptors, and those people can see a wider variety of colors as a result. they don't have a wider range of colors, but are able to distinguish between two different colors that look basically the same two people with just three photoreceptor colors.