Question:

What is the colour of the shortest wavelength observable light?

Answer:

Keeping in mind the actuality that the higher the frequency the shorter the wavelength the names of the kinds of electromagnetic radiation on either side of visible light in the electromagnetic spectrum may help keep the order of the colours in terms of wavelengths or frequencies in mind. Ultraviolet significance above violet gets its name because its frequency is even higher than the frequency of violet light the highest frequency (and thus the shortest wavelength) in the visible spectrum.

Infrared significance below red gets its name because its frequency is even lower than the frequency of red light the lowest frequency (and thus the longest wavelength) in the visible spectrum.