The refractive index of a medium is dependent (to some extent) upon the frequency of light passing through, with the highest frequencies having the highest values of n.

For example

in ordinary glass, the refractive index for violet light is about one percent greater than that for red light.

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The Refractive Index of a medium depends upon the refractive index of the surroundings, optical density, wavelength of the light, and temperature.

ND17-1-2023