B Speed of Light in Various Mediums

This may be a rather ridiculous inquiry, but Google queries haven't helped much.

As I understand it, different colors (wavelengths) of light move at the same speed in a vacuum, which together make up what is often called "white light." However, when light enters the Earth's atmosphere, its speed slows slightly. It would seem to me that the speed of the light itself isn't really changing, but that the way various wavelengths react with different mediums could make it appear as such. Such as light traveling through a see-through gem might not really change the light's speed, but that the light simply has more to reflect around from inside the gem, and it makes it seem like the light slowed.

Exactly what factors go into various mediums and different wavelengths that affect light's speed? Thanks.


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Speed of light depends upon the density of the medium.

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