Which colors of light represents the lowest visible frequency?

Red

Explanation:

Red is a colour which has the lowest frequency. Violet has the highest frequency. Frequency has a direct relationship with energy. This means the higher the frequency, the higher the energy. Red has the lowest energy of all the colors too.

The frequency and Energy has an inverse relationship with the wavelength.

However Red has the longest wavelength of about 620 - 780 nanometer.