Electrophysics engineer here to lay down a harsh truth: You've been lied to about the Blue hues. They are not so vast as you have been led to believe. There is a large group of hues which don't really belong to Blue, and should be thought of as their own distinct color family.
Specifically, I am here to tell you these two colors are NOT both Blues:
Only one of them is Blue (left); the other is Cyan, a hue that is even more distinct from Blue than Orange is from Red. If you believe that Orange as a full fledged color, you really must count Cyan as a full fledged color as well.
First a little color (simple) theory background. Colors come in different hues, which are usually defined as color groupings. There is a color "Blue" and a hue "Blue" which covers many colors. There is not a "Ultramarine" hue, as this color resides within the Blue hue "group." A tint is a color which has white added to it. A shade is a color that has black added to it, or had its saturation lowered.
There are two kinds of colors the human brain can see: Spectral and Mirage, and two ways humans reproduce colors: Additive and Subtractive.
Color Types
Spectral colors (Objective colors): These colors come directly from light sources, such as the sun, light bulbs, flames, etc. and the reflected light off objects in the world. Sunlight emits all wavelengths our eyes can see, When all of these wavelengths are reflected back into our eyes from a white object (DON'T LOOK AT THE SUN) all the light-sensitive cells in our eyes are stimulated at once and our brain sees white. Most objects only reflect a sub-set of the white light that hit them; the rest of which is retained as heat energy. A rainbow allows us to see all the spectral hues spatially separated when white light passes through spherical rain drops and is refracted in differing amounts based on the color.
Spectrum of sunlight through a prism onto a white envelope (Dec 2024)
Note: True Indigo and Violet are not able to be shown on an RGB screen.
Mirage colors (Subjective colors): Spectral hues do not include all the colors our brains see! Most importantly there are no magenta or purple hues in the spectral
colors, as these are "imagined" colors our brains create when differing
amounts of blue and red light stimulate our eyes simultaneously and the
green-sensitive cells are not stimulated. If any colors differ between what each person's brain sees it would probably be the colors in these "mirage" hues.
Mirage hues are created by the brain when light-sensitive cells in our eyes are stimulated using multiple different colors. For instance, the yellow color you see on your PC or cell phone screen is actually red and green lights on your phone shining simultaneously (and at similar brightness levels). The same is also true with cyan colors (green and blue lights) and magenta (blue and red lights). In fact, every color you see on your TV, PC, or phone that is not red, green, or blue is a "mirage" hue that your brain is inferring (or inventing, as is the case with magentas and purples). This can be easily seen if you put a drop of water (ONLY A DROP) on your screen and look at non-RGB colors.
Note: There is a common misconception that different colors of
light somehow "combine in mid-air" to create other wavelengths of light.
For instance, the mistaken notion that red and green light waves
"combine" to make yellow light. This is incorrect. While light waves can
interfere with each other to cause amplitude modulation (i.e, bright and dim bands of light) they DO NOT combine in frequency modulation
to make different colors of light.
Frequency modulation in FM radio
comes from the radio signal source changing frequency, not a combination
of radio waves in mid-air. If we could see radio waves FM broadcasts
would look like a color changing light source next to a constant
(carrier) source. Perfect for midnight raves!😎 Meanwhile, AM radio
would look like a light house, with a single dimming and brightening
source.
Color Reproduction
Additive color reproduction (RGB) is made from light sources such as a cell phone, TV, movie projector, PC screen, etc. Using only three primary spectral colors of light: Red, Green, and Blue (RGB) a computer screen can fool your eyes into seeing all the colors of the rainbow. This is because our eyes have three kinds of light-sensitive cells (cones) which are each most sensitive to different wavelengths of light, which roughly correspond to the spectral colors of
- Red
- Green
- Blue
By varying the stimulation of the three cones in your eyes with the three different light sources, additive color screens can fool your brain into seeing almost the colors of the rainbow a(sans indigo and violet) and most of the mirage colors as well.
How Red Green and Blue lights can combine to create different colors.
Red + Green = Yellow. Red + Blue = Magenta. Green + Blue = Cyan.
Subtractive color reproduction (CMY) is made out of light filters, materials which only allow specific wavelengths of light to pass through them. When these are overlaid onto a white background (often some sort of paper) they subtract some of the wavelengths which make up the white light bouncing off the paper and deliver narrower spectral colors to our eyes. By using only three primary filters:
- Cyan: Blocks Red light, passes Green and Blue light
- Magenta: Blocks Green light, passes Red and Blue light.
- Yellow: Blocks Blue light, passes Green and Blue light
artists can create all the colors of the rainbow and the mirage colors too! Cyan and Magenta together only pass Blue light, Magenta and Yellow only pass Red light, and Yellow and Cyan only pass green light. Not quite the Primary Colors they teach in Kindergarten, but similar in concept.
How Cyan, Magenta, and Yellow filters can combine to create different colors.
Cyan + Magenta = Red. Magenta + Yellow = Green. Yellow + Cyan = Blue.
Note: Some digital projectors also include filters to include Yellow and/or Cyan light in addition to Red, Green, and Blue light to try and do a better job at reproducing yellow and cyan colors. (They cannot include Magenta light as this doesn't exist!) This can sometimes produce distracting visible artifacts of cyan and yellow light if you move your eyes to quickly back and forth.
Cyan Is a Separate Hue from Blue
If you have made it this far you have probably noticed how distinctive Cyan is from Blue in both of the color reproduction methods. We all agree that Yellow is a separate hue, why can't we all admit the plain fact in front of all our faces: Cyan is it's own hue separate from Blue.
Take a look at this diagram:
Here is the same graphic, but with the RGB values for each color:
Orange is much closer to Red (1/4 of way between red and yellow), and is actually much more similar to Chartreuse and Spring (both often considered greens), Azure (almost universally considered a blue), and Rose (usually thought of as a red).
Purple is also interesting as usually it is thought to be right in between Red and Blue, but is actually much closer to Blue. This is probably because people are measuring it as half-way between Cyan and Red! Wrong, people. Wrong. Wrong. Wrong.
Why are We Like This?
So what gives? Why is Cyan so ignored? I think there are several reasons for this.
The "Blue Sky" Theory
Theory: So many people associate the color blue with the sky, so to suddenly realize it is often closer to Cyan than Blue would be too much for people to deal with.
Let's look at some facts.
Here is a photo I took of the spring sky in Seattle in April 2025. If we sample the sky and take a look at the color we see it is somewhere between Cyan and Azure.
The pure (normalized) color is made up of more than 35% green, which is
much closer to the 50% green of Cyan than the 0% green in Blue, and only
slightly closer to the 25% green in Azure.
Could you argue that the color of the sky is closest to Azure? Sure. Could you argue that Azure is a Blue hue? Yeah. But you gotta admit that whatever color the sky is in this picture, it is much closer to Cyan than pure Blue! Food for thought.
The "No Green Sky" Theory
Theory: The sky usually never contains pure greens, and so it is psychologically difficult for people to recognize that on a bright summer day the sky could, in fact, be 50% green.
Another "sky theory" and the one I think is most correct.
Green lies right in the middle of the visible spectrum, and so it makes up many of the "mirage" versions of spectral colors (for instance mirage yellow is, in fact, 50% red and 50% green), and unlike in RGB screens, a mirage blue can also exist in the sky that is 50% green and 50% violet! Because white light from the sun covers a wide spectrum when the atmosphere scatters shorter wavelength light (blue and violet) the atmosphere glows blue.
This scattering makes the sun itself slightly yellow in the sky because if you smear all the blue and violet light across the sky, the remaining light (Red, Yellow, and Green) looks like spectral yellow (Yellow light) and mirage yellow (Red light + Green light). As the sunlight is filtered through more and more of the atmosphere (near sunrise and sunset) the light from the sun is more and more filtered and the remaining light (Red, and Yellow) makes the sun look orange from spectral orange and mirage orange (Red light + Yellow light), then finally almost pure red right as the sun passes the horizon.
Unfortunately green being in the middle of the spectrum hardly ever gets to be it's own color in the sky because it either gets lumped into white when red and green is near same levels, or into either a yellow or cyan mirage color when either blue or red is much lower (depending on the position of the sun and the part of the sky you are looking at). Therefore, the colors of the sky get broadly grouped into blue (sky), yellow (noon sun) and red/orange (sunset sun/sky). This is why most plants have settled on green leaves, because they can absorb direct light from the sun (red) and indirect light from the sky (blue), but also reflect the middle of the spectrum (green) to keep cool.
All this to say that because the cyan and blue parts of the sky are usually present together in a smooth gradient, and so it often just gets lumped together as "blue" for simplicity. *Le sigh.*
We are Just Like Pre-Orange Civilizations
The most interesting part about living in a pre-Cyan point in human history is that we have a pretty close corollary into understanding why "red-heads" are not called "orange-heads."
The RGB/CMYK model gives the proper orders of colors, and puts Cyan on the same level as Red, Yellow, Green, and Blue
Secondary colors
From: https://en.wikipedia.org/wiki/Secondary_color#RGB_and_CMYK
I disagree with the above list of colors calling the color between Blue and Magenta "Violet" in
RGB - it should be "Purple" to indicate it is fundamentally different
than "Violet'. Purple is NOT a mirage version of Violet as mirage
Violet would require a visible color of shorter-wavelength, but spectral Violet
is the limit of human vision, and colors in a violet hue would still require a spectral Violet
light of shorter wavelength; which is NOT present in RGB screens. Fight
me, Wikipedia!
What To Do, What To Do?
Unfortunately, as with the continued use of the Imperial measurement system in the United States, the unrecognized status of Cyan as a distinct different primary color from Blue is probably something we will have to live with. However, we don't have to live in darkness. We can educate our fellow citizens and maybe someday Cyan will finally get the attention it deserves in art classes and elementary schools!
Someday Cyan will get it's day in the sun; even though it has always been right there in front of us in the rainbow.
