Which color has the highest frequency?

In VIBGYOR. It has colors ordered from highest to lowest frequency.

              Violet > Indigo > Blue > Green > Yellow > Orange > Red

That says Violet has the highest frequency.

We know, Speed of light = Frequency x Wavelength

=> As frequeny is inversely proportional to wavelength i.e, as frequwncy goes high wavelength goes down.

So, the violet color has the highest frequency.