color theory

The True Primary Colours: Unravelling the Mystery and Settling the Debate

If you’ve been following our social media posts, you may have noticed a recurring debate in the comments section: what exactly are the true primary colours? As passionate enthusiasts of all things STEAM, we feel it’s finally time we settled this debate once and for all. So, buckle up and join us on a colourful journey as we delve into the world of primary colours, explore the differences between RGB and CMY, and even take a trip down memory lane with RBY. And to top it all off, talk about why CMY Cubes are Important for Subtractive Colour Mixing.

RGB vs CMY: A Tale of Two Colour Models

Before we dive into the nitty-gritty, let’s first establish that there are two main colour models at play here: additive and subtractive. Each model has its own set of primary colours, which are used for different applications. 

Additive Colour Model (Digital Displays) 
Primary Colours: Red, Green, and Blue (RGB)

When it comes to digital displays like computer screens and televisions, the additive colour model reigns supreme. This model uses red, green, and blue (RGB) as its primary colours. By combining these colours at different intensities, the additive colour model can produce a vast spectrum of colours. When all three primary colours are mixed at full intensity, they create white light. 

Subtractive Colour Model (Printing and Painting)
Primary Colours: Cyan, Magenta, and Yellow (CMY)

In the realm of printing and painting, the subtractive colour model takes centre stage. This model relies on cyan, magenta, and yellow (CMY) as its primary colours. These colours are combined to absorb certain wavelengths of light and reflect others, generating a wide range of colours. When all three primary colours are mixed, they theoretically produce black. However, due to practical limitations, a separate black ink (key or K) is often added, resulting in the CMYK colour model used in printing.

Some simple examples include:

  1. It is difficult to mix cyan, magenta, and yellow inks precisely in equal proportions, which can result in a colour that is not quite black but rather a dark muddy brown.
  2. When printing large areas of solid color, the amount of ink required to create a deep black color using only CMY inks can cause the paper to become saturated and potentially cause smudging or other printing problems.
  3. The cost of using a separate black ink is often less than the cost of using additional amounts of the other three inks to create a darker shade of black.

The CMY Conundrum: Debunking the RBY Myth

Now that we’ve established the two primary colour models, let’s delve into the fascinating world of traditional primary colours for painting and art education: red, blue, and yellow (RBY). Despite their prevalence, these colours are not truly primary, as they cannot generate all possible colours when combined. This is where the CMY model comes into play, providing a more accurate method for subtractive colour mixing.

One basic example of how RBY is limited in its ability to generate all possible colours how you can’t make cyan or magenta with any combination of red, yellow and blue. But you CAN make red, yellow and blue with cyan, yellow and magenta. 

Another is in the RYB colour model, when you mix all three primary colours together, you get a muddy brown or black colour. In contrast, in the CMY colour model, when you mix all three primary colours together, you get black. Sarah Renae Clark. (n.d.). Advanced Colour Theory: RYB vs CMY.

So why is the CMY model more accurate?

The answer lies in the fact that cyan, magenta, and yellow are better suited to absorb and reflect specific wavelengths of light. This allows them to create a more comprehensive range of colours than RBY ever could. However, due to the longstanding history of RBY in art education and cultural significance, this trio of colours continues to be taught in many art classes.

As we’ve discussed, the CMY model is more accurate and efficient for colour mixing than the RBY model. But the question still remains: how did RBY become so deeply entrenched in our understanding of primary colours in the first place?

The historical prominence of RBY can be traced back to the early days of colour theory, when artists and scholars alike were attempting to understand the nature of colour and its applications in art. The influential artist and writer Johann Wolfgang von Goethe, for instance, propagated the idea of RBY as primary colours in his 1810 work, “Theory of Colours.” This idea was further popularised by the works of Michel-Eugène Chevreul and Ogden Rood, both prominent colour theorists of their time.

Despite the continued presence of RBY in art education, there is a growing movement to shift the focus towards the more accurate and versatile CMY model. By embracing the subtractive nature of the CMY model, artists can achieve a broader range of colours and better understand the underlying principles of colour mixing.

Check out this great video by Sarah Renae Clark!

The True Primary Colours: A Scientific Explanation?

After discussing the different colour models and their primary colours, you may be wondering: what are the true primary colours?
The answer is not as straightforward as you might think. In fact, the concept of primary colours is not a scientific one, but rather a human construct based on our perception of colour. That being said, there are a few criteria that can be used to determine what we consider as primary colours.

Firstly, primary colours should be pure, meaning they cannot be created by mixing other colours together. Secondly, they should be able to combine to create a wide range of other colours. Finally, they should be applicable across different colour models and mediums.Using these criteria, we can identify different sets of primary colours depending on the colour model being used.

In the additive colour model, the primary colours are red, green, and blue (RGB). These colours can be combined to create all other colours visible on a digital screen.In the subtractive colour model, the primary colours are cyan, magenta, and yellow (CMY). When combined, these colours can absorb all wavelengths of light except for those that create the desired colour.

It’s important to note that in printing, black (K) is often added to the CMY model to improve the quality of the final product, resulting in the CMYK model.

As for the traditional RBY model, while it is still taught in art education, it is not considered a scientifically accurate set of primary colours. As we’ve discussed, RBY cannot create all possible colours and is therefore limited in its applications.

Introducing CMY Cubes: A Visual Aid for Subtractive Colour Mixing

One innovative tool that is helping to bring the CMY model to the forefront is the CMY Cube. This captivating and educational device demonstrates the principles of subtractive colour mixing in a tactile and visually engaging way.

Each face of the translucent cube is coated in electromagnetically subtractive materials, which at first, appear as cyan, magenta, or yellow. When light passes through the cube, it interacts with the subtractive materials on each face, effectively demonstrating how different combinations of primary colours create a vast array of secondary and tertiary colours.

Why CMY Cubes are Important for Subtractive Colour Mixing

CMY Cubes are not only a visually stunning representation of the subtractive colour model but also serve as an invaluable educational tool. By allowing users to see and manipulate the primary colours in real-time, CMY Cubes provide a hands-on approach to understanding the intricacies of subtractive colour mixing.

This hands-on experience can be particularly beneficial for artists and designers, who often work with physical media and rely on an intuitive understanding of colour theory to create visually harmonious and impactful work. By using CMY Cubes as a reference tool, these professionals can develop a deeper understanding of the subtractive colour model, which in turn can improve their ability to mix and apply colours effectively.

True Primary Colours: Demystifying the RGB vs CMY Debate:

While the concept of primary colours may seem simple, it is actually a complex and nuanced topic. The debate over primary colours may never truly be settled, but by understanding the differences between the RGB and CMY colour models and the limitations of the RBY myth, we can gain a deeper appreciation for the complexities of colour theory. The introduction of the CMY Cube as an educational tool has brought a new level of interactivity to the study of subtractive colour mixing and has the potential to revolutionise the way artists and designers approach colour theory. 

Ultimately, by delving into the science and art of colour mixing, we can gain a deeper understanding and appreciation for the beauty and complexity of the world around us.

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As an illustrator and graphic designer I was taught that Red Blue Yellow were primary for opaque pigmented colours (paint). where the colour range is expanded further by the addition of opaque white and black.

CMYK are the primary colours for printing, where the CMY ink colours are translucent (light passes through the ink and reflected off the white of the paper, the whiter and more reflective the paper the better the result).
As previously mentioned in the article, the addition of the ‘Key’ colour which is opaque black, where the light is absorbed, not reflected.
In addition print technology used half tones, which is a grid of dots. During the printing plate production the image/photograph is projected through the dot filter and the image is converted from continuous tone to half tone, where the image dots on the plate are of various sizes which give varying intensity of colour for each individual CMYK plate. Further more each separate plate has the half tone (dot) screen rotated a specific angle so that the ink dots do not directly print over the top of each other but are offset. I can’t remember exactly why this is but think it is due to a more even coverage of ink that reduces the amount of pure white of the medium (paper) to reflect, except where needed when white or ‘gradients’ to white are needed for the white/light areas of a photograph. In this process light travels through the layers of translucent ink and is reflected back through the overlaying colours of the ink to produce the full range of colours reflected back to the eye.

I hope this makes sense?

One last thing, this type of printing is called offset litho (lithography). It can be taken a step further to create even better results by the ‘Gravure’ printing process, where the ‘dots’ are now ‘cells’ with the addition of varying depth which allow varying amounts of ink to be laid down, which controls the density of the colour along with the size of the dot/cell. This produces a much finer detailed print with continuous tone which is more like a true photograph. This process is expensive and usually only used for such things like postage stamps and reproduction of fine art, where the detail and continuous tone is required and affordable.

As graphic design moved on from print to the addition of screen viewing (light) for the new fangled internet and the new interactive medium of web sites, graphic designers had to start to think in the realm of Red Green Blue, as that is how screens projected colour, either by means of Cathode Ray Tubes or later Flat Screens. So when a designer is producing artwork for web sites or screen advertising the art work colours needed to be managed as RGB.
For printing, the colour needs to be seperated into CMYK for magazines, leaflets and posters etc. When an image is initially scanned electronically it is scanned in RGB (ideal for screen application), but for print, the RGB needs to be converted into CMYK. In applications such as photoshop or InDesign, the RGB can easily be converted into CMYK channels for print application. The result is that the image on the screen is instantly flatter with reduced colour hues and less contrast. This now gives a more accurate representation of the finished printed product which cannot compete with the colour range and intensity of RGB light as used by electronic screens.

There is not one primary set of colours but three, depending on the purpose.

RBY: for pigment such as paint (with the addition of White and Black to increase the colour range).

CMYK: For ink printing such as mainstream printing methods of Off-Set-Litho and also Gravure.
(silk screen is altogether different and can combine opaque and translucent inks).

RGB: For electronic screens (TV screens, both CRT and Flat LED/LCD screens and Advertising boards).


Ian Jakeway

Such a beautiful explanation of colour theory and well done.
I think we can all agree that colour will always reveal the presentation of magic and wonder.

-Jadine aka ‘aging hairdresser’ 😀

Jadine Morris

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