The electromagnetic spectrum consists of radio waves, microwaves, infrared waves, visible light waves, ultraviolet waves, X-rays, and gamma rays. Of these seven types, humans can only sense visible light waves, which have a wavelength ranging from 380nm to 760nm. Considering that the whole electromagnetic spectrum has wavelengths ranging from hundreds of thousands kilometers long (radio waves) to less than a hundredth of a nanometer (gamma rays). In other words, the electromagnetic spectrum contains wavelengths spanning 20 orders of magnitude and humans (without technological aid) can only detect less than half of one order of magnitude.
Of our five senses, only one deals with electromagnetic radiation. Our eyes allow us to see wavelengths in what we call the visible spectrum. The cone cells in our eyes allow us to detect the differing wavelengths of visible light and we perceive these differences as different colors. We have three types of cones in our eyes: one for short wavelengths, one for medium, and one for long. The combination of varying levels of activities of the three types of cones allows us to see the whole color spectrum.
Here’s an interesting thought: you cannot imagine a color that you haven’t seen. How would you explain the concept of color to someone who is blind? How would you describe the color red?
So what if humans could detect other types of electromagnetic radiation? What exactly would we see? The disappointing answer is that we don’t know. We could sense sources of electromagnetic radiation. If you walked outside, you would sense ultraviolet radiation from the Sun and radio waves from broadcasting towers and your phone. You would sense microwaves from your microwave oven while preparing lunch. We might see more “colors” depending on the wavelength of the electromagnetic waves that we see.
Thermal imaging cameras that use infrared radiation to sense the environment assign colors to various wavelengths of infrared. The X-rays that are emitted from space have varying wavelengths as well, and astronomers use false color to differentiate the wavelengths. In reality, the other types of electromagnetic radiation do not actually have color, we just assign wavelengths from the visible spectrum to illustrate the difference in wavelengths of other types of waves. Trying to visualize other types of radiation is like thinking of a color that is not on the visible spectrum: you just can’t do it.
Cosmos Commentary 
