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Additive vs Subtractive Colours

Updated: May 6, 2021

Colour. It's its own language, it has the power to evoke an emotion or a sensation, it can be attractive or off-putting, it can denote a specific message and it can compliment itself when placed with other colours. It is such a clever tool that is both useful and pleasurable, if you're fortunate enough to perceive them.


While colours can have meaning, this varies wildly throughout history, between cultures and personal perception. Our understanding of colour is constantly evolving and the colours we admire or despise tend to shift through trends.


For the record, I don't believe there are any colours we should despise, only that they may not have been used in the correct context.

A spread of Pantone colour cards, featuring a spectrum of colours from red, orange, yellow, green, blue and purple.

How is colour perceived?

When thinking about applying colour, it's important to understand how colour is perceived and, more accurately, how we process different wavelengths of light and interpret them as colours.


Light is extremely complex, travelling from short wave gamma rays all the way to long wave radio waves. Within these frequencies is a very narrow range called the visible light spectrum. The light waves within this spectrum are what our eyes interpret as colour.

Wavelength diagram displaying the range of the visible spectrum.

Light waves touch a surface, are absorbed by the surface and the reflected light bounces off the surface and into the cones in our eyes. These waves are then interpreted by our brains as colour.


If we take a blade of grass as an example, it is hit by all colours of the visible light spectrum. The blade of grass will absorb the red, yellow, orange, blue, indigo and violet light and reflect back to our eyes the waves of green light. These light waves are processed by our eyes and interpreted as green by our brains. The interesting thing about this process is, green is the only colour the blade of grass hasn't absorbed and has instead reflected back.


Perception

As you begin to think on the mechanics behind how we perceive colour, it becomes a bit existential. There are lot of elements in this process which can manipulate the colour we actually see, from the quality of the rods and cones in our own eyes, to trying to question what every colour together except green could look like and the fact that people's cones may behave differently to yours and experience a completely alternative colour.


Beyond the differences in our own biology, our brains play a fundamental part in manipulating our perception of colour. Context can play a big role.

Illusion image featuring 3 squares of red, blue and green colours with a smaller grey square in the centre

You'll have likely seen illusions, like the image above, that demonstrate how easily our brains can be tricked into perceiving colours differently. The three squares in the centre of each block are the exact same shade, yet look completely different when placed next to another shade. Colour relationships can greatly influence how we register a particular hue.


The same can be true of lighting. The particular environment in which you view a colour can dramatically alter how it's perceived. This is especially the case when viewing a colour on a bright screen, say a pink cardigan versus seeing that same pink cardigan on your friend at a dimly lit bar. The temperature of the lights in the bar my trick your brain entirely into thinking the cardigan wasn't pink at all. Throwback to that blue/gold dress debate to give you a sense of how lighting can alter our brains perception of colour.


Additive Colour Mixing

If you've ever looked through a prism, or seen a rainbow, what you are seeing are wavelengths of light dispersed into their separate colours. All waves of light combine to make white light and this white light can be split through a prism to reveal the constituent wavelengths.


Violet and green light combine to make blue, green and red light combine to make yellow and red and violet light combine to make magenta. Violet, red and green all combine together to make white. As the light is combined, it becomes brighter.

Diagram displaying red, blue and green light waves overlapping to create white. Caption reads "Additive Colour Mixing becomes brighter as the available light is combined".

Subtractive Colour Mixing

If you've ever mixed paints together, the idea of mixing colours together to make white seems utterly backwards. As paints are mixed they become darker and murkier. Often the pigments have to be mixed with white in order to achieve a paler shade.


The reason for this is as you add physical paints together, you are subtracting from the visible light spectrum. Each pigment only reflects a portion of the visible light, as you mix them together, more and more wavelengths are subtracted.


If you continue to mix red pigment with blue pigment it will get increasingly darker until you have a dark plum. Whereas, as mentioned above with Additive Colour Mixing, this would instead result in a bright magenta as you are adding two wavelengths together. Subtraction and addition are resulting in the inverse effect when mixing light waves vs physical paints.

Diagram displaying cyan, magenta and yellow pigments overlapping to create black. Caption reads "Subtractive Colour Mixing becomes darker as the available light is reduced".

It's all in your head

Colour is an extremely complex subject. Understanding which colours work well together, how colours affect mood, how the perception of colour can be changed by context, these are just some colour concepts and they don't stop there.


There's also the practical application of how to mix colours, what colours you can and can't achieve due to the limitations of subtractive colour mixing etc.


It isn't always an exact science, it is an art. Having a deeper understanding of the science behind colour is an important way to remove creative blockers. The science is complicated and maddening. Do not let this deter you from experimenting, throwing the book out of the window and exploring the colours you want to explore. It's also one of the best ways to learn.


References

The Secret Lives of Colour - Kassia St Clair

https://wordery.com/the-secret-lives-of-colour-kassia-st-clair-9781473630819

BBC Bitesize - What is Colour?

https://www.bbc.co.uk/bitesize/topics/zw982hv/articles/zcj73k7

Light Waves Diagram CC BY-SA 3.0

https://commons.wikimedia.org/w/index.php?curid=2521356

Contrasting Colour Combinations by Akiyoshi Kitaoka

https://www.researchgate.net/figure/Colour-contrast-using-the-same-colour-combinations-as-fig-1-The-small-square-in-each_fig2_228490244

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