Which color in the spectrum of hydrogen has the lowest frequency?

The visible color in the hydrogen spectrum with the lowest frequency is red. Red has the longest wavelength, and therefore the lowest frequency, of any visible color. Hydrogen emits red at a wavelength of 656.2 nanometers.

Hydrogen emits light at lower frequencies than human eyes are capable of seeing. The lowest frequencies that are not visible to humans in the hydrogen emissions spectrum are to be found in the infrared. On the rare occasion that an electron jumps to the n=7 energy level in a hydrogen atom, emission can go as low as 12,400 nanometers, or a frequency of 2.418 x 10^13 Hertz.