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I was taught that the colors we see are results of the corresponding wavelength, but each wavelength also has a distinct frequency since speed of light is fixed for a specific medium (same goes for sound).

$$ c = νλ,$$

where $c =$ speed of light in vacuum, $ν =$ frequency of light, and $λ =$ wavelength of light.

Now, I have also learnt that while the frequency remains unchanged in a refraction - both wavelength of light & speed of light change. Meaning - if the color of light depends on the wavelength, the colors of the spectrum shifts slightly depending on the refractive index, for medium to medium (but will go unnoticed to human eye).

As I understand it, if light travels from one medium 1 (say vacuum) to a medium 2 with refractive index µ, then -

cλ2 = vλ1 and c = µ*v

where - λ2 & λ1 are wavelengths of the same wave in medium 2 & 1 respectively, µ is the refractive index of medium 2 wrt 1 and v is the speed of light in medium 2.

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    $\begingroup$ Note that what reaches your retina goes its final path through one and the same medium: the vitreous humor. This makes the wavelength of a particular frequency fixed. After this the job is on the retinal pigments, which of course work by absorption, which depends on frequency. $\endgroup$
    – Ruslan
    Commented Nov 1, 2023 at 11:42
  • $\begingroup$ Perhaps this answer (and the question) is helpful: physics.stackexchange.com/a/48244/313612. There are quite a few relevant questions and answers already here, findable by searching a bit. $\endgroup$
    – Ed V
    Commented Nov 1, 2023 at 12:42
  • $\begingroup$ Referring to "absorption, which depends on frequency." – By leaving the fluid/different medium the photon resumes not only the speed it once had but also its "old" wavelength? Pure conclusion on color being frequency not wavelength dependent wouldn't be possible. There is not enough space in between the media to do this? - In a physiological way, absorption might depend on wavelength as with longer wavelength lesser the photons that come close enough to be absorbed. Is there reference for all this? $\endgroup$
    – Peter Bernhard
    Commented Nov 13, 2023 at 17:33

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