It is very common for us humans to assume that the so-called color spectrum contains all the colors that exist in the world. And it is true - that is, all the colors that exist in the human world. In reality, there are plenty of colors that simply cannot be perceived by the average human eye.
For the sake of most arguments, color is simply considered the range of light across the electromagnetic spectrum that humans can see. In other words, colors are actually how our brains – with the help of our eyes – interpret a stream of tiny packets of energy radiating at different frequencies in a wave pattern. But let's be honest: that's a mouthful.
What we really need to know is that our eyes, in all their complexity, can only interpret a limited range of light. That means there are colors we can't see due to a phenomenon known as the opponent process. These are known as "forbidden" or "impossible" colors.
The opponent's trial
The “oppositional process” theory states that the colors we see are paired in opposite shades. When we perceive these opposite colors (e.g. red-green, blue-yellow, black-white), they automatically cancel each other out. This process suggests that thislimitation in the way the human eye sees colorsmeans that some colors are simply imperceptible.
However, some vision scientists argue that these so-called "impossible" colors are simply intermediate colors between two others. Nevertheless, some experiments have shown that colors are perceived that are not normally visible to the human eye.
Impossible colors may not exist as individual colors like red, blue and green, but several studies have now shown that the brain can be 'tricked' into seeing something unfamiliar and appreciating a wider spectrum of colors than we thought possible.
But first things first...How can we even see color?
How do we see color?
Our eyes classify light based on its wavelength - which can vary from many meters between each 'wave' peak to as little as the diameter of an atom.
The entire electromagnetic spectrum ranges from high-energy, short-wavelength light waves, such as cosmic rays and gamma rays, to low-energy, long-wavelength light waves, such as radio waves.
The light we can see –known as the visible light spectrum– ranging from violet light, which has a wavelength of about 400 nanometers, to red light, which has a wavelength of about 650-700 nanometers.
How the eye works
Our vision works by capturing light that bounces off objects around us. This light enters our eyes through the cornea (the transparent outer layer) and the pupil at the very front of the eye. The cornea bends light into the eye, while the pupil expands or contracts to let in more or less light.
From here, the refracted light hits the lens inside, which angles it and focuses it on the retina at the back of the eye. The light is detected by special cells at the back of the retina and information is sent via the optic nerve to the brain, where the image is processed and interpreted.
The retina consists of light-sensitive cells called rods and cones. These cells send information to the nerve cells in the inner retina: rods are responsible for our perception of light and dark and our peripheral vision; cones ensure that we can perceive color.
There are three types of cones, each sensitive to different wavelengths of light. We havemore cones sensitive to red light than any other type, which means that our vision is best suited to warmer colors such as red, yellow and orange. But our cones are limited in detecting light waves that fall within the range of 400 nanometers and 700 nanometers.
For example, the wavelength of gamma rays is approximately the length of the nucleus of an atom, which is far too short to be received by our cones. At the other end of the spectrum, radio waves are too long, as long as two Empire State buildings stacked on top of each other!
As you might expect, other animals have different types of cones that allow them to see a wider or narrower range of the electromagnetic spectrum. For example, dogs are more limited in the wavelengths – and therefore colors – they can see, while butterflies can see ultraviolet light, which humans cannot detect. However, the prize for the most far-reaching vision goes to the mantis shrimp, which has twelve different types of cones.
The impossible colors
Now that we have a clearer idea of how the human eye works to detect color, we can begin to understand a little more about these so-called "impossible" colors.
As we mentioned above, the human eye has three types of cones that allow us to see a certain range of light and thus see colors in the electromagnetic spectrum, that is, the spectrum of visible light. These colors are blue, green and red.
But of course we see much more than just these three colors. This is because there is an overlap in the wavelengths of light covered by the cone cells. For example, white is not a wavelength of light; instead, we see it as a mixture of different colors.
The antagonistic way in which colors are presented and the aforementioned resistance process ensure that our eyes cannot perceive certain colors at the same time. These arelight versus dark, red versus green and blue versus yellow.This is why – if you have light hair, you may be asked to use purple shampoo to banish yellow tones from your hair.
Therefore, the colors 'bluish yellow' and 'greenish red' are the so-called 'impossible' colors that we cannot see.
Is it possible to see impossible colors?
The hostile process theory of color perception was developed in the 1970s and suggests that it is impossible for humans to perceive the impossible colors. However, since then there have been a number of studies, starting witha famous experiment from the 80s– have claimed that it is possible to 'trick' the brain into seeing these colours.
In this experiment – which is not recommended to try at home – subjects stared at an image consisting of two strips: one red and one green. The subjects' heads were stabilized with a chin rest and their eye movements were monitored using a camera. The images moved with their eye movements to ensure that their eyes remained fixated on the opposite colors and that they received a continuous wavelength of light.
The results of the experiment were surprising, even to the researchers. Under the right conditions and in the right amount of timethe border between the opposing colors seemed to gradually dissolve, and the so-called forbidden or impossible colors appeared.
Our eyes, with their more than two million working parts, allow us to see a huge range of colors, but it is not the only way we see the world. Perhaps a day in the life of a mantis shrimp would open our eyes to other ways of seeing and how colorful the world can be.
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