Seeing Invisible Colors

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.

Pigment Sensitivity Knowing Neurons

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!

Mantis Shrimp Knowing Neurons

Would it ever be possible for us, as mammals, to see these invisible colors?  Perhaps.  Recently, gene 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.

Monet's Lilies

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?



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.

Joel Frohlich

Joel Frohlich is a postdoc studying consciousness in the lab of Martin Monti at UCLA. He is interested in using brain activity recorded with EEG to infer when a person is conscious. Joel earned his PhD from UCLA in 2018 studying EEG markers of neurodevelopmental disorders in the lab of Shafali Jeste. You can also check out Joel's blog Consciousness, Self-Organization, and Neuroscience on Psychology Today. For more about Joel's research and writing, please visit Joel's website at

3 thoughts on “Seeing Invisible Colors

  • July 2, 2015 at 7:14 pm

    What if your red is my blue and my blue is your red? How would you ever know?

    We already have evidence for this, don’t we? I am pretty sure you have heard of this:

    I kinda believe that all this comes down to language. Consider an experiment where people are asked to describe what they are shown in “great” detail. Lets say that they are shown an object that looks like a normal tree and they are asked to describe it. Now I have used the word “tree”, but what is it that constitutes a tree? There are so many aspects to a “tree”, so when someone is asked to describe it in great detail their descriptions might differ. Some might miss out details that others find and vice-versa. But at the end, they all agree that they are looking at a tree. Somehow our language has come to a point where we describe an object of such complexity as a tree using a single word. But when you dig into the details, different people will have different descriptions. So I believe that the aspect of our perception that we have come to call ‘color’ is also because of language. Its just that some aspects of our perceptions have a single word to describe them. But this breaks down in some cases and we have a situation like the Dressgate.

  • August 1, 2015 at 4:55 am

    Also doesn’t mention that humans actually DO have four chromatic cones…well, some us do. We all have 3 types of cone-cell (S, M & L)…two of these are coded for by genes located on the x-chromosome.
    In most women they have two copies of the L cone gene – but only one copy gets expressed – or they both get expressed but the resultant cones are so similar in receptivity, the brain nixes it out. They get a slightly broader expression of colour in the orange-red range, because the sensitivity wavelength is a little wider..but not really much difference – this may be stems from an evolutionary advantage to telling slightly different shades of colour – women seem better able to use skin-colour cues to realise a child is sick etc.
    However, in some women the difference between those L cones is larger, and instead of cancelling it out, the brain percieves the different colour ranges…effectively meaning they are true tetrachromats…

    This is important because, besides my fiancee being able to yell at me because “those two wallpapers are COMPLETELY DIFFERENT..what are you, blind?!?”, it also means the plasticity of the brain and optic nerve is high enough to be able to process 4 cones without difficulty…
    This means either through engineering and gene therapy, or direct mechanical manipulation (stimulating the retina via artificial implants one day), we can potentially widen our visual spectrum by an unlimited amount…

    • August 1, 2015 at 1:58 pm

      Thanks for your comment! We might be covering this soon in an upcoming post … stay tuned.

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