Some images on the electromagnetic spectrum can be seen by the naked eye. However, most can’t. This has to do with the types of rays used as well as the frequency and wavelengths. Whenever we use our vision to view light in wavelengths, we are seeing colors.
The colors and objects that are visible by the naked eye on the electromagnetic spectrum include those that are near ultraviolet and near infrared. The near ultraviolet rays have a frequency of about 300 THz and they have a frequency of 1 wavelength.
The near infrared rays have a 3000 THz just like the near ultraviolet rays and they have either 1 or 10 wavelengths. Others that are not visible include ionizing radiation and microwaves.