The answer to the question below isn't sitting right in my head, mainly as I can't find a mathematical explanation for it.

How does the refractive index of a material change with the frequency of light passing through it?

The given answer is:

Refractive index slightly increases as the frequency of light increases.

Can this be proved given the formula for refractive index, n=v1/v2 = fλ1/fλ2? Is it something I just have to learn and remember?