Additive_main.jpg
Kate Smith
Print

In print, Cyan, Magenta, and Yellow pigments, (CMY colour model) are known as ‘printer’s primaries’ and are generally printed using a method called half-toning.

Paint

The traditional set of ‘painter’s primaries’, are Red, Yellow, and Blue paint (RYB colour model). A combination of these paints, when physically mixed in certain proportions, produces a wider set colours.

Digital

In an additive colour model, Red, Green, and Blue light (RGB colour model) is superimposed onto each other used to produce different colours.

RAL
PANTONE Matching System
Additive_main.jpg
Showcase 30 Sep 2015

Additive and Subtractive Colour

Colour is infinitely complex and understanding why we have different sets of primary colours, as well as understanding the functions of each set, can strengthen our mastery of colour in design.

Most of us were children when we first learned about colours. We had boxes of crayons and sheets of construction paper, full of possibilities. Grade school art teachers taught us about primary colours and secondary colours, often showing us a colour wheel that demonstrated the relationships among colours. Those simple lessons shaped our interactions with colour through our childhoods. 

Fast forward and we now have a far more complex understanding of colour. Not only do we as designers realize the power of colour as a design principle, but we’ve also learned primary colours aren’t quite as simple as we thought they were. 

In fact, there is more than one set of primary colours, and more than one way of creating colour. 

We’re going back to school, with a topic you may have avoided. As it turns out, understanding the different sets of primary colours requires a small physics lesson. For design purposes, the most important differentiation between primary colour sets is defined based on whether you’re talking about subtractive colour or additive colour.

Subtractive Colour

We’ll start with subtractive colour, since it is closer to what we learned as children. Subtractive colour refers to combining paint, ink, or dyes to create a wider range of colours. Why do we call it subtractive, when what we’re really doing is adding pigment? That’s where the physics comes in. The way subtractive colour works is by absorbing colour, so the hues not absorbed are perceived as the visible colour by the eye. 

There are two different sets of subtractive primary colours. The painter’s primaries of red, yellow, and blue (RYB) are the ones we learned in school. 

The RYB primaries overlap to create secondary colours of violet, orange, and green. This colour wheel was widely used prior to our modern colour theories, and there  are interesting historical variations of this colour wheel based on regional availability  of pigments.

 The most commonly used subtractive colour model is the printer’s primary array of cyan, magenta, and yellow (CMY, or CMYK, when you add black or the key colour). Again, this colour model is subtractive because the amount of one colour used determines how much of a complementary colour is reflected, and therefore perceived by the eye. The amount of magenta present determines how much of its complement—green—you see. Likewise, cyan complements red and yellow complements blue. Both subtractive colour models begin with white. When all three primaries overlap—and therefore absorb all colours—the convergence is black. As it turns out, starting with white and moving toward black is precisely the opposite of the way additive colour works.

Additive Colour

Additive colour is used in digital and television screens, and is based on the physics of coloured light and, more importantly, how we perceive it. When the additive—or light —primary colours of red, green, and blue (RGB) are projected in overlapping circles, they create the additive secondary colours of cyan, magenta, and yellow. 

Interestingly enough, the way additive colour actually works on a computer screen, for example, doesn’t actually depend on overlapping colour, but rather proximity. When you look closely, really closely, at a screen, you see that each pixel is actually comprised of sub-pixels of red, green, and blue. Creating the colours your eye perceives is a result of illuminating pixels in close proximity that your eye, in turn, blends.  Light a red and blue sub-pixel, and your eye, not powerful enough to individually perceive such tiny spots of light, sees magenta differently than subtractive colour. When all three additive primary colours overlap, they create white, as opposed to the black obtained by combining the subtractive primaries. The relationship between additive and subtractive colours isn’t precisely opposite, though. When you look at both colour models side by side, you’ll note the same colours are  present, but in different relationships.

Colour Systems

So why does it matter whether a designer understands the differences between subtractive and additive colour? It can be as simple as realizing the colours you see on your computer screen, for example, are physically created differently than the colours you see on paint chips. Those differences matter when you’re working with multiple media and concerned with challenges like accurately depicting and duplicating colours, not to mention tackling problems associated with moving colours into different textures, patterns, and materials.

RAL

RAL

Let’s look at the RAL colour matching system, for example. RAL, originally developed in Germany in 1927, made it possible for collaborators on a project to use numbers—provided both parties had the colour standards, of course—to discuss colours with precision. Prior to RAL, the parties would have had to exchange samples. How does RAL relate to subtractive colour? Items officially made using RAL standards are absolutely precise, whereas items made using different standards will often reveal colour variations in different lighting. That means the precise shade and amounts of colours absorbed are different. Colour consistency matters, so much that approved RAL products produced after early 2013 bear  a hologram as a mark of their authenticity.

Munsell Colour Theory

Likewise, Albert Munsell developed his colour theory in an attempt to create an even more precise language for talking about colour. His use of three distinct colour continua—hue, value, and chroma —equipped him with a system by which he could describe a much fuller range of precise, reproducible colours. Like RAL, Munsell applications are largely subtractive in nature, and having a common language for describing colour yields consistency in design projects.

Pantone Matching System

PANTONE Matching System

The PANTONE Matching System (PMS) has made the greatest strides toward colour matching across additive and subtractive sources. One of the big challenges in colour matching on computers is that additive colour varies depending on the hardware. Many software users now specify colours using the PMS in order to minimize the differences in the perceived colour from device to device. PANTONE Personal Colour Calibrator™ even permits designers to input information about their computer monitor make and model, and the display will be optimized for colour accuracy.

Natural Colour System (NCS)

Even NCS, the Natural Colour System that’s used in Sweden, Norway, and roughly ten other countries, plays into a discussion of additive and subtractive colour. NCS uses six elementary colours arranged in complementary pairs—black-white, redgreen, and blue-yellow—and the relationship among them to precisely describe more than ten million colours. While both the additive RGB model and the subtractive models (CMY and RYB) rely on the eyes’ colour receptive cones, NCS relies on the retina’s ganglion cells.

Do you have to understand the difference between retinal ganglia and colour receptive cones in order to be a great designer? Of course not. Understanding the physics of how and why we came to have more than one model for primary colours, however, helps you frame, present, and collaborate on projects in a way that makes your colour decisions more precise.

Contributor: President and Chief Color Maven of Sensational Color, Kate Smith is an internationally renowned colour expert, sought out for her ability to guide businesses on how to use colour to gain recognition and generate revenue. www.sensationalcolor.com


Images


• Nicholas Roerich » commons.wikimedia.org/wiki/File:Chud_ Departed_Beneath_the_Earth.jpg

• Colourfeeling » commons.wikimedia.org/wiki/File:RAL_ K5_F%C3%A4cher_rgB.jpg