Wavelength corresponds to colour, but how?

Question

Between the input (wavelength) and output (colour), what occurs? How do we receive 650nm, for example, and interpret it as red? What even is red? What is colour, really?

In: Physics

Answer 1

Beautiful GIF:

[https://en.wikipedia.org/wiki/Wavelength#/media/File:Light_dispersion_conceptual_waves.gif](https://en.wikipedia.org/wiki/Wavelength#/media/File:Light_dispersion_conceptual_waves.gif)

And helpful chart:

ELI5: Your eye has three alarms. One goes off for those tight short-wavelength frequencies, one for the middle, and one for the middle-high.