What would the world be like without color? Imagine you are a neurophysiologist, who studies color perception. You know that light is a wave and that humans perceive color according to differential activation of color receptors, known as cones, in the retina. You know that red cones are sensitive to long wavelengths, green cones are sensitive to medium wavelengths, and blue cones are sensitive to short wavelengths. There’s just one issue: your entire life, you have been confined to a dark room where your only access to the outside world is a black and white television monitor. You have never seen color.

Now imagine, like Dorothy leaving Kansas, you step outside this black and white room and see color for the first time. Do you learn something new? This scenario was first posed by the philosopher Frank Jackson as a challenge to purely physical views of the universe. Colors are like labels used by our brain to indicate the wavelength of light reflected or emitted by an object. Although the light represented by colors can be described in entirely mathematical and physical language, color itself is an ineffable quality that cannot be described without direct experience.

What would it be like to see “invisible” new colors? Many birds, insects, and fish have a fourth type of cone sensitive to ultraviolet (UV) light, i.e., light with a wavelength shorter than blue light. Because each cone can detect about 100 different variations of color, these animals with an extra type of cone can see 100 times as many colors as humans. For us, it is impossible to imagine how such animals visually experience their world. But don’t envy them yet. The animal with the most sophisticated color perception is the mantis shrimp, a flamboyant crustacean with sixteen distinct types of cones. The mantis shrimp can perceive 100 septillion (1026) times as many colors as humans. This is an astoundingly large number – a billion times larger than the age of the universe in seconds!

Would it ever be possible for us, as mammals, to see these invisible colors? Perhaps. Recently, geneA sequence of nucleic acids that forms a unit of genetic inh... therapy was used to bestow colorblind squirrel monkeys with the red cone necessary for red-green discrimination. All male squirrel monkeys are congenitally red-green colorblind, but with this gene therapy, adult male monkeys are able to distinguish red from green. Furthermore, the retinas of treated monkeys respond electrically to red light post-therapy. Theoretically, similar gene therapy could be used to give humans new cone cells for perceiving colors in the UV spectrum. However, the lens of the eye would first need to be replaced, as it serves as a filter blocking UV rays. Interestingly, when the lenses of the eyes are removed for cataract surgery, light in the near UV can potentially be perceived as light blue or light violet. This might explain why French impressionist painter Claude Monet, who had surgery to remove his cataracts, painted water lilies bluer following the operation.

Of course, true perception of a new color would require the introduction of a fourth type of cone cell, but the medical and ethical consequences of such a drastic procedure have yet to be considered. Meanwhile, like Frank Jackson’s scenario of a neurophysiologist living in a black and white room, we remain entirely ignorant of what it might be like to experience new colors. Even knowing how other humans experience color requires the assumption that the minds of others are similar to our own. What if your red is my blue and my blue is your red? How would you ever know?

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References:

Jackson, Frank. “What Mary didn’t know.” The Journal of Philosophy (1986): 291-295.

Marshall, Justin, and Johannes Oberwinkler. “Ultraviolet vision: The colourful world of the mantis shrimp.” Nature 401.6756 (1999): 873-874.

Mancuso, Katherine, et al. “Gene therapy for red–green colour blindness in adult primates.” Nature 461.7265 (2009): 784-787.

Images by Jooyeun Lee and from skepticalartist.

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