What is colour?

January 21, 2022

Colour does not exist, but is created in our brains. In order to see colour we need light, an object and our eyes. Colour arises in the presence of light. Whenever light falls on an object, some of the rays are reflected by the object and the remainder is absorbed. The part that is reflected, determines the colour. 

PERCEIVING COLOUR

Our eyes cannot perceive the light that is absorbed by an object. An apple, for example, absorbs all colours, except green. Because the green is reflected and is captured by our eyes, we see the green colour of the apple. 

If all the light rays are absorbed, we get black, and when all the light rays are reflected, we see white. Thus, a black object absorbs all colours and is therefore sometimes described as colourless. For the same reason, black objects also soak up more heat than white ones, because white reflects all colours or wavelengths. 

Light

Light reflectionThe most ideal light for seeing colour is diffuse daylight, when the sun is more or less behind the clouds and it is slightly rainy. This produces the most truthful colours. In artificial light, it is more difficult to perceive colour in a precise way. The main reason is that artificial light, such as that of a fluorescent lamp, is often tinted blue or red. A colour can therefore look different under various light sources. Even natural light such as candlelight emits an abundance of yellow and red, because the light source does not contain enough blue. Metamerism is the phenomenon in which colours appear to be the same in a certain light, but turn out to be different with other lighting circumstances. That is why it’s important to compare colours in ideal and comparable lighting circumstances.

Object

The presence of an object is the second condition for perceiving color. The object itself may either emit light, reflect light or a combination of both. Also the surface of the object is important for seeing colour; a shiny object reflects light differently than an object that is matte.

Eyes

The third condition for seeing colour, is that the rays should be caught by the eye. The light rays enter the pupil, through the lens and the eyeball and land on the retina. The receptors in our eye, consisting of rods and cones, ensure colour perception in our brains. The extent to which the cones vibrate is translated by our brains into different colours and shades. The rods, in turn, are sensitive to the intensity of the light. Consequently, they cannot tell the difference between colours or hues that have the same intensity of light.

Cones

Human eyeWe have about six million cones: an average of two million red, three million green and one million blue. The colour that we see is formed by these three impulses. Red, green and blue (RGB) are therefore called the optical primary colours. People with colour blindness have deficient colour receptors.

Rods

Aside from cones, our eye possesses some 120 million rods, which are unevenly distributed across our retina. The rods contain a visual pigment that changes structure, depending on the light intensity, and so transmits a signal to the brain.

The human eye has a particularly large adaptability, which is why we’re able to compensate for extreme differences in brightness. Thus if, for example, we drive through a long tunnel and our eyes have adjusted to the darkness, we can see normally again in bright sunlight relatively quickly.

RESEARCHING COLOUR

Research into colour began around 1700 when Newton deflected a light beam with his prism, making the different colours of the spectrum visible. The British physicist demonstrated hereby that white light is composed of all the colours of the spectrum. This discovery laid the foundation for the understanding of color as a physical phenomenon. His research is the point of departure for various models and theories that have since been developed to understand and measure colour.

Light travels as a wave

In the investigation of colour, the question whether light should be considered as a wave phenomenon or whether it could better be explained as a particle stream has always been a central one. At the beginning of the last century, physicists Max Planck and Albert Einstein provided a breakthrough. Just like sound, their research confirmed, light travels as a waveThis made it possible for the first time, to accurately measure and get to the bottom of the phenomenon of colour and light. 

Researching color

Specifically, a wave has a certain length (which is expressed in nanometers, nm), which is dependent on the frequency (which is expressed in hertz, Hz) of its vibration (which is expressed in milliwatts, mW). The frequency of the vibrations determines how strongly a particular colour is reflected to our eyes. We call this aspect the colour strength or chroma. For example, yellow-green has a maximum vibration at a wavelength of 550 nm. It is important to know that the range of human perception lies between 380 nm (UV, ultraviolet) and 780 nm (IR, infrared). This has to do with the maximum vibration frequency that our eyes can perceive. Colours strong in grays provide a hazy image to the brain. 

The scientifically proven Colour Navigator System solely clusters the useful colour range. In other words: all colours that are beyond the reach of our perception are omitted and the colours that do give sufficient impulse to our brains are clustered.

In a wavelength curve, the relationship between the vibration and the length of a wave is displayed. Every colour has its own, unique wavelength curve. A horizontal curve representing our visible spectrum, is black at 0 mW, white at 100 mW and gray at mid-height.

The colours of the spectrum can also be arranged in a colour wheel. In principle, this gives the same representation as the horizontal axis of the wavelength curve, but then in a curved line around an axis. The colour wheel is used in a counterclockwise direction: the colours range from red at 30º, yellow at 90°, green at 150°, cyan-blue at 210°, blue at 270° and magenta-purple at 330°.

USING COLOUR

When working with colour, we distinguish two methods: additive and subtractive. On a monitor, display or television screen, colours consist of red, green and blue (RGB). But when it comes to printed media, prints or paint for objects or dyes, cyan, magenta and yellow (CMY) form the basis to compose colours. We call working with RGB the additive use and working with CMY the subtractive use of colour. 

Additive RGB

Additive – RGB

In the additive system, red, green and blue are the primary colours. They are displayed by using a light source and monitor, and consist of red, green and blue percentages, with which millions of colours can be formed.

By mixing two additive primary colours in equal proportions, secondary colours arise; in the additive system, these are cyan (green + blue), magenta (red + blue) and yellow (red + green). An equal amount of the three colours results in white. 

Because the RGB system is connected with a display on a monitor, colour differences will be perceptible among the different types of screens. A monitor is therefore best calibrated or adjusted to an appropriate colour profile. 

Substractive CMY

Subtractive – CMY

We call mixing colours with paint or ink subtractive colour mixing. Cyan, magenta, and yellow are in this case our primary colours. If we mix two of these in equal proportions, we get red (magenta + yellow), green (yellow + cyan), and blue (magenta + cyan), this time called the secondary colours.

We can make colours lighter by adding white or make them grayer by adding black. In this way, different shades of the same colour arise. In theory, using cyan, magenta and yellow, every other colour can be made, but in practice it is impossible to mix neutral gray or pure black. 

MIXING COLOR

We use primary and secondary colours for mixing. When we mix colours subtractively, for example with paint or ink, there are several options to achieve almost the same result. “Almost”, because our brains experience the different ways to mix the same colour differently.

Primary colours

Primary colours are colours in their pure essence: yellow, cyan and magenta. These colours cannot be created by mixing other colours.

Secondary colours

Secondary colours are mixed forms of two primary colours in a certain proportion, such as green, orange and purple. Primary and secondary colours are pure colours. They are located at the edge of the colour wheel and have a maximum saturation of their chroma.

Tertiary colours

Tertiary colours can be created by mixing certain colours:

  • Three primary colours or a combination of a primary and a secondary colour in which the primary colour is not present.
  • A primary colour with black.
  • A primary colour and its complement.

Mixing color

Option 1 produces the least beautiful result, because, by using three primary colours, this causes our brain to see more grayscale. Option 2 is the least expensive way of mixing.

The best result – which our brain perceives as most beautiful – is created when mixing complementary colours (see later), such as in option 3. By applying this way of mixing, the primary colour, to which the colour to be mixed is closely related, constitutes the starting point. By then adding the complementary colour, the main colour will stand out more and get more character. The created colour will give our brain a more pure colour impulse.

Mixing colorMixing colorMixing color

Trichromatic black is the black that occurs when mixing the three primary colours. The result is very dark anthracite (almost black). To make a colour grayer or to mix colour, it is better to use trichromatic black or anthracite and never use true black (ink black). This way the colour stays pure.

DESCRIBING COLOR

Over the course of time, all kinds of systems and theories have been developed to arrange and map colours in a universal, easy to use way. Well known examples of colour systems are Munsell’s colour atlas and its derivative colour systems such as HSV and HCL.

Munsell Colour System

The Munsell Colour System was developed at the beginning of last century by Munsell, the American inventor and artist. In this system, 1500 colours were visualised in a sphere around an axis of grayscale values. Horizontally, there was a gradient from neutral gray to full saturation. Munsell called these values: hue, chroma and value


Munsell Color SystemHue stands for colour tone and represents the location of a colour on the colour wheel. One speaks of the hue- or colour angle, which is expressed in degrees.

The strength of a colour is called chroma by Munsell. Maximally saturated colours are the most intense colours.

Value indicates the brightness: the amount of light that is reflected by a colour.

White, for example, has the greatest brightness and black the least.

  

It was significant that Munsell discovered that the full chroma of individual colours could be achieved at different locations in the colour area. Yellow reaches its optimal colour, for example, at a much higher saturation than red. This has led to a visual representation of an asymmetrical sphere or spinning top.

The Munsell Color System was created empirically and is mainly based on how we perceive colour. It has a less mathematical and scientific basis, but provided important insights into saturation and is still a recognised color system. The company that Munsell founded in 1918 still exists.

CIELab

CIELab is a colour system that was launched in 1976 by the Comité International de l’Eclairage (CIE). The commission was established as an independent forum that, among other things, had as its objective the development of an international standard. The CIE model approximates the human perception of colour as closely as possible and constitutes the basis and standard on which our Color Cluster System was developed.

Revised standard

Color observer

 

CIE developed a first step towards a standard colour observer in 1931 and presented a revised version in 1976, in which the most important adaptation was to turn the colour wheel, so that red came to be at 0° and yellow at 90°. This was because the colours enter our brains in a specific sequence (first red, then green and then blue). Red produces the most powerful impulses and is therefore the strongest colour, followed by green and blue.

Numerical values

A colour observation will translate a colour between the receptors and the brain with distinctions between light and dark, indicated by a vertical L or luminosity axis, which represents the brightness, and between red, green, blue and yellow, indicated by the horizontal a and b axes, which represent the observable colour space.

MEASURING COLOUR

As we just saw, colour is indicated by three values: the L-value indicates the brightness on a scale from 0 (black) to 100 (white), the a and b values define the colour. We can measure these three values with a colorimeter or spectrophotometer that is converted to Lab values. By combining the coordinates of the three axes, we arrive at a clear position of a colour in the colour sphere, which in reality is not a perfect sphere, given the differences in saturation, as discovered by Munsell.

 

HSV and HCL

HSV en HCL are two very simple models for defining colour for desktop applications and graphic programs, closely corresponding to the way we perceive colour. To some extent, it is comparable to Munsell’s system because it takes hue, chroma and value as its starting point on three similar axes in order to define a colour.

In HSV, these are hue, saturation and value. In HCL, they are determined by hue, chroma and luminosity. Moreover, HSV also exists under the name of HSB, hue, saturation, brightness, and HCL also commonly appears as LCH, luminosity, chroma and hue. The values of HSV and HCL are comparable. HSV is often used in graphics software. By specifying a hue and saturation rate, it is possible to set the brightness using the scrollbar and thus to select millions of colours.

The digital era demanded a universal colour coding, which, inter alia, could easily be used in HTML. Thus, the HEX value was created as the standardised translation of the RGB. It is a value from 0 to 255, noted in a hexadecimal system consisting of 16 symbols: the digits 0 through 9 and the letters A (= 10), B (= 11), C (= 12), D (= 13), E (= 14) and F (= 15).

HEX calculation for blue

HEX calculation for blue #239CF5
35/16 = 2 remainder 3 or 23
156/16 = 9 remainder C (= 12) or 9C
245/16 = F (= 15) remainder 5 or F5

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