Is Pink Real?

A recurring theme on this blog are the subjects of categorization and semantics. And a particularly fascinating oddity shows up when we explore these concepts as applied to the world of color.

For within the world of color, it is sometimes said that the color pink is not real. And the reason why is, whether "real" or not, truly weird and mind-boggling. Because how pink comes about as an experience in the human mind is unique among the main primary and secondary colors.

Why is pink unique? We first get a hint of this by noting that pink is not present in rainbows. The main colors of the rainbow are red, orange, yellow, green, blue, indigo, violet (often abbreviated as ROYGBIV). They correspond to how colors exist in nature. Color is made up of
different kinds of light. Each color represents a certain wavelength of light, and those colors exist along a spectrum.

Each color in the spectrum has its own wavelength associated with it. Seems like that might explain everything all neat and tidy. But then we realize ... where's pink? If you're trying to find it on the spectrum, you won't be able to. It's not there. There is no single wavelength of light associated with pink. The color pink, in this sense, truly does not exist.

So, where the heck does pink come from and what even is it?

The answer lies in the fact that humans don't "see" each wavelength individually. We detect light when it enters our eyes, and within our eyes are receptors called cones. There are, for most humans, three types of cones and each is tuned to specific wavelength ranges. Each cone has a spot on the wavelength spectrum spot where it alone activates brightly while the other two cones don’t, and these correspond with the colors red, green, and blue. Red light activates the red cone. Green light activates the green cone. And our brain produces the experience of seeing red, green, and blue. 

Note: The above paragraph is somewhat oversimplified for clarity and brevity compared to rather more complex underlying biology

What happens when a wavelength color without its own associated cone enters the eye? It "activates" multiple cones simultaneously, and our brain creates a new color experience. Yellow is the main color between red and green. Yellow wavelength light with activate both red and green cones strongly, and this produced the experience of yellow.

The tricky addition to the puzzle comes when more than one wavelength of light enters the eye simultaneously. If a source of green light and a source of red light are both shined into the eye simultaneously, what happens? Well, just like yellow light alone, biologically the green and red cones both become activated, and so our mind also perceives this experience as yellow.  

Yellow light = red and green cones firing = experience of yellow color

Simultaneous red + green light mix = red and green cones firing = experience of yellow color

As a side note, this is how digital screen displays produce color. Each display is in fact a set of red, blue, and green light emitters placed next to each to form one pixel. Producing yellow means having the desired yellow pixels shine red and green light at your eye.

We still haven't explained pink. But here's how we'll get there. 

We just mentioned that mixing red and green makes yellow. Yellow, as a wavelength, is roughly halfway between the red and green wavelengths. Another important color, teal, is what is perceived when we mix blue and green. Some cultures consider teal as it's own distinct color rather than simply being a shade of blue, and the color theory here lends some credence to that notion.

The remaining cone combination is red and blue. Looking at our light wavelength spectrum, what's halfway between red and blue? Green. So what does mixing blue and red light in our eyes produce? You guessed it, it makes pink!

Because we have a green receptor in our eye, our eye knows that green isn't present when there's only blue and red light. So, our psyche decided to create a "new" and different color instead and that's the color we experience as pink.

Astute readers might wonder why such a thing as "violet" exists in the ROYGBIV rainbow colors, and does in fact have a wavelength associated with it while pink does not. Answer is contained in a postscript note below, but the short version is that there's an extra little wrinkle of cone sensitivity biology involved.

As a disclaimer, will note that the above is a somewhat simplified model of the most complex puzzles within human biology. The biology of color is extremely complex and beyond the scope of this article. I wanted to cover the basic because, bringing us back to the primary focus of this blog, we can now end with a short exploration of the semantics and concept construction of the term color. And what that means about how to think of the question "is pink real?".

What pink is not is a direct representation of a singular photon of light, nor is it a collection of photons all with similar properties. 

What pink can be a direct representation of, in the physical world, is a material object that, when white light is shined onto it, will emit back out a combination of wavelengths that a human eye will translate into the mind experience of pink.

Semantically, we can now understand that the term pink is being used to describe all three of....

1) The experience of color within the human mind

2) The combinations of light wavelengths that, upon hitting a human eye, can trigger the human experience of pink

3) The collection of objects that, when struck with white light, will reflect back out the wavelength combinations explained in definition 2

What 1, 2 and 3 are revealing are three different subdivisions of "reality". There is the world of the human mind. There is the world of energy (heat and light). And there is the world of material objects. Each have their own "realness" to them, but each of these worlds are such different sorts of things.

The color pink is an excellent window into exploring how complex it can be to categorize each of those worlds and how different each world is.

A further interesting point is that definitions 2 and 3 are, in part, dependent and conditioned on their relationship with being a human experience. Pink objects matter as a category primarily because it's humans who see pink as its own color, so that grouping of certain objects as pink is meaningful to us. It shows us that scientific grouping and categorization can be biased toward what is being interacted. Ideally we're in theory heading toward catalogue every thing that matters to every other thing, but it's interesting to think on what biases may be present in this regard. Humans, quite naturally, find use in and will tend to build tools, including scientific tools, built to accommodate human perspectives. 

Footnote on Violet and Purple

One question left unanswered by the above article is why violet / purple exists at the shorter wavelength end of the visible light spectrum. To be perfectly honest, it's an answer I've been able to fully answer with confidence yet. I do have one partial explanation that seems likely, but I haven't been able to verify that it's truly the answer or how it relates to the rest of the above. As mentioned above, color biology is astoundingly complex!

What I have read is that the red cone, as seen in the graph below, is the only one that has two sensitivity peaks. This still means that it's only red, green, and blue wavelengths where solitary cones are being primarily activated. But it also means that there's a quirky little extra range to the left of blue where both the blue cone and the secondary smaller red cone range are both being activated. 

This stimulation produces the color violet, and so it can be said that the violet is a real singular wavelength of light.

We also can touch on why I keep saying "violet" here instead of purple. The terms "purple", "magenta", "violet", and "pink" all seem to occupy a similar-ish space in this area of blue + red cone activation. Wikipedia defines purple is any of a variety of colors with hue between red and blue, with violet often toward the darker blue and black shades and pink toward the lighter red and white shades. Magenta, roughly, seems to typically be used to refer to the middle purples between violet and pink.

In color theory, it is the term magenta, along with cyan/teal and yellow that make up the three primary colors needed for color printing (as can be seen on home printer cartridges). I chose to use the term pink in this article as a stand-in for magenta since it's a more commonly used color in everyday term usage, and it's the magentas and pinks that's don't have singular wavelengths unlike the oddity that is violet.

We can also note, while we're on the subject of terms and shades, that in the ROYGBIV rainbow set of colors the "blue" in that sequence is traditionally referring to teal/cyan, while indigo refers to a darker blue that represents the blue color associated with the blue cone. What could perhaps be called "true blue".

Further Research

Left unanswered from my research so far are the reasons for two of the remaining most distinct colors - brown and orange - being so distinct in their own right.

For a look into why yellow is the most distinct fourth color after blue/red/green, and why both red-green and blue-yellow are opposites, read more here.