For example, [this colour wheel has 12 sections](https://www.spectrumnoir.com/wp-content/uploads/2017/04/Colour-Wheel-2.jpg) and performs a full ‘loop’ for lack of a better term (i.e. starts at red, traverses to the polar opposite, and returns the natural way). We can see every one of these clearly, and every colour in between those two colours as it’s simple a mixture, or a mixture of a mixture, or so on. So how can a colour exist outside this wheel?
In: Biology
There aren’t.
(Assuming you were just using that image as a general example of a colour wheel. Cuz we can definitely see more colours than those on that wheel literally.)
Colours do not exist out there in the world. Colours only exist in your eyes/brain. There are more *wavelengths* of light out there than humans can detect. But colour is NOT an inherent property of light. Colours are created in our minds.
Other answers are talking about our eyes having only three colour dectection cells. And yes, you see red when ~680 nm light hits your eyes. However, you ALSO see red when light of all wavelengths except ~510 nm hits your eyes (i.e. red = white – green). Colours are not inherent to the light frequency, but instead they are made by how our eyes and brain react and interpret the light falling on our eyes. Pink doesn’t even have an associated wavelength of light. You can *only* see it when you have light of all wavelengths but ~580 nm hitting your eyes.
Physically our eyes only react to wavelengths of light in the 400 to 700 nm range. Though of course this isn’t a hard limit to wavelengths. Light can have higher or lower wavelengths. We don’t detect all of them because it wouldn’t be useful: the atmostphere blocks out most other wavelengths before the light reaches the ground.
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