What determines the color of light in frequency?

Answer 1

Probably the right answer is your eye determines the color by showing different frequencies differently. Higher frequencies shows up as what we call blue and lower as what we call red. All an accident of nature. The eye could have been differently constructed and you might not see visible light at all, only x-rays, or radio signals.

Answer 2

two separate things here
frequency is the wavelength - color is a perception the brain and the eye uses not a measurement of any type ( except the way the eye perceives different frequencies )

Answer 3

The wavelength of the light. Longer wavelengths are more towards the red part of the spectrum, the shorter wavelengths are towards the blue part.

As the wavelengths become longer or shorter than what we can perceive as light, they are called infrared or ultraviolet respectively.