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Refractive index is the ratio of the vacuum speed of light to its speed in the medium, n = c/v. Light at 2.0e8 m/s gives n = 1.499, typical of crown glass. Frequency is unchanged on entering the medium, so the wavelength shortens by the same factor - 589 nm sodium light becomes 393 nm inside the glass.
Refractive index
n = c / v
Wavelength inside
lambda(medium) = lambda(vacuum) / n
No. Colour follows frequency, which does not change. Only the wavelength contracts, which is why the light looks the same on emerging.
The phase index can be, in plasmas and near absorption lines, but the group velocity carrying information never exceeds c.