Colour Theory

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Colour Models

 

The most popular model used for helping people understand the mixing of coloured paint is the 'RED YELLOW BLUE'  system. The CYAN YELLOW MAGENTA model, used mainly by printers, can also be used to explain colour mixing but is not as easily understood.

This tutorial uses the RED YELLOW BLUE Model.

 

Primary, Secondary and Tertiary colours

 

There are three Primary colours: RED, YELLOW and BLUE.

Primaries - Red, Yellow and Blue

Secondary colours are colours produced by mixing two primary colours. The secondary colour is midway between the two primaries. e.g. Mixing Red with Yellow will produce Orange, Mixing Blue with Yellow will produce Green and mixing Red with Blue will produce Violet.

Secondary colours mixed from primary colours

Tertiary colours are colours produced by mixing a primary colour with one of its secondary colours. i.e. Mixing Red with Orange produces a Red Orange. Mixing Blue with Green produces a Blue Green. Mixing Yellow with Orange produces a Yellow Orange etc.

Note: Some art/colour references may use the term 'tertiary' to refer to a mix consisting all three primary colours but this is not generally accepted.

tertiary
tertiary

An even wider variety of hues can be achieved by varying the relative quantities of the primary colours.

The Colour Wheel

The Colour wheel is a useful pictorial representation of the spectrum of colours and can be used to simplify the understanding of the interaction of colours used in a painting. It can also help with selection of a palette of colours, colour mixing, the natural greying of colours, and colour perspective (also called aerial perspective). The simplified wheel opposite consists of the primary, secondary and tertiary colours explained above. The three primary colours Red, Yellow and Blue are shown in the large circles. Between each of the primary colours are the secondary colours, shown in the middle sized circles, which result from mixing the two adjacent primaries. The tertiary colours obtained from mixing the primaries with their respective secondary colours are shown in the small circles. As the colours progress around the wheel in any direction, each one is a gradual change from its adjacent colour.
The colours on the right of the wheel shown opposite are known as cool colours - colours which are blue or have a leaning towards blue (yellow-green to blue-violet)
The colours on the left, are known as warm colours - colours which are red or have a leaning towards red (yellow-orange to red-violet)

Colour Wheel
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Complementary Colours

Complementary colours are those which are opposite each other on the colour wheel. For example, red is opposite green. Green is made from the other two primary colours so it contains no red. When these complementary colours are put together in a picture the result is striking - think of poppies in a green field. Each colour makes the other 'sing' and have vibrancy.
Each primary has a secondary colour which is its complementary and vice versa:

  • Orange is the complementary of Blue.
  • Green is the complementary of Red and
  • Violet is the complementary of Yellow,
complementary


Tertiary colours also have complementary colours but in these cases the colours opposite will also be tertiary colours:

  • Yellow-Orange is the complementary of Blue-Violet
  • Yellow-Green is the complementary of Red-Violet
  • Red-Orange is the complementary of Blue-Green etc.
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Shades


When complementary colours are mixed together,  they have a neutralising effect on each other so the resulting colour is duller (greyer) producing a shade of the colour. Adding red to green neutralises the green and continued addition of red will eventually result in a colourless grey or even black. What is really happening is that all three primaries are being mixed together which, in the right proportions, theoretically produces black. Further addition of red will produce a greyed red (brown). This neutralising effect is shown on the extended colour wheel opposite where the colours become duller or greyer as they approach the centre of the wheel. The colours produced in this way are often referred to as 'Neutral Colours'
So, when you need to produce a natural dulling or greying effect on green, such as the shadow area of a tree just look at the colour wheel and - add a little red! If it's a blue green tree - add a little Red Orange.
If you need a subtle grey for cloud shadow, use the blue used for the sky and add it's complementary.
Using a complementary colours in this way produces a more natural and exacting dulling than using black or grey paint. It will keep your colours clearer, fresher and more alive.

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neutral colours

Tints

Tints of a colour are produced when white paint is added to that colour. In the case of traditional English watercolour, the white of the paper is used as the 'White paint' component and tints are produced by adding more water to the colour allowing more light to be reflected from the surface of the paper through the transparent colours.
In the diagram opposite, the colour wheel is shown inside the white circle. Tints produced from the colours in the colour wheel are shown in the outer ring of colours.

Tints
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Paints and the Colour Wheel

Pigments used to manufacture paints do not normally produce pure red, blue or yellow and most contain traces of one or both of the other primaries. Because of this it is difficult, if not impossible to produce the full spectrum of colours that are present in nature by using a single Red, Blue and Yellow. The answer is to select a palette of colours which will allow mixing of a much wider range of colours but will also be restricted enough to make it easy to become familiar with them and understand the interactions. The colour wheel has already been used to show the progression of warm to cool colours and it also shows that each colour such as blue or yellow has  warm and cool versions of the colour. For example:

  • 'blue violet' is a warm blue as it has some red content;
  • 'yellow green' is a cold yellow as it has some blue content in it;
  • 'red orange' is a warm red as it has no blue in it; but
  • 'red violet' is a cold red as it has blue in it.

All the examples above are tertiary colours and many of the pigments used in the manufacture of paint also produce tertiary colours - so an 'optimised palette' should consist of two versions of each primary:

  • a warm (Leaning towards Red)
  • a cold (Leaning towards Blue

One such palette is given below though there are many alternatives to the specific colours chosen here.
YELLOWS: Cadmium Yellow - (Warm Yellow, Yr), Lemon Yellow (Cold Yellow, Yb)
REDS: Cadmium Red (Warm Red, Ry ),  & Alizarin Crimson (Cold Red, Rb)
BLUES: Ultramarine (Warm Blue, Br),  & Cerulean Blue (Cold Blue, By )
The 'Yr' symbols means Yellow with a trace of red, i.e. primaries yellow (dominant) and red (trace) are present etc.

 

And now for a bit of simple algebra that will brighten or dull your colour mixing and even your day! - don't worry, it won't hurt.
When you mix two or more colours  together, you will know before you mix them whether you will get a subdued colour or a bright colour!
If the mix contains all three primary letters it will be subdued to some extent depending on the relative quantities of the primaries.
If the mix contains only two primary letters it will always be bright.
Lets look at some examples:

Cadmium Yellow mixed with Cadmium Red is Yr + Ry, result - bright orange (contains only reds and yellows)

Cadmium Yellow mixed with Alizarin Crimson is Yr + Rb, result - slightly duller orange (as it contains all three primaries -i.e.  just a trace of blue - the complementary of orange)

With these near primaries in the optimised palette, it's not likely that they will produce significantly subdued colours or greys by mixing any two of them together as the trace colours are relatively small in quantity compared to the dominant primary colour. Neither will mixing only two such colours produce mud.
However, by mixing three together, particularly if they include all three dominant primaries, subdued colours (greys) will be produced - again this is shown by the presence of three upper case letters. e.g:
Cadmium Yellow, Alizarin Crimson and Ultramarine = Yr+Rb+Br = high possibility of subdued colours. YRB present.

Cadmium Yellow, Lemon Yellow, and Ultramarine = Yr+Yb+Br = low possibility of subdued colours YYB present.

Note: In watercolour, the opacity of the paint also plays a part in a mixtures tendency to produce muddy colours.

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Cadmium Yellow

Cadmium Red

Bright Yellow red
Duller Reds and Yellow

Alizarin Crimson

Cadmium Yellow

Subdued mix

Cadmium Yellow, Alizarin Crimson Ultramarine

Cadmium Yellow, Lemon Yellow & Ultramarine

Cadmium Yellow, Lemon Yellow & Ultramarine

Of course you can use the 'mixing code system' with any colour in your palette to help in assessing it's potential mixing properties. If the colour is a near secondary, designate it with two upper case letters. e.g Orange = YR, Green = YB, Violet = RB
As you have seen from the colour wheel charts above, some paints will contain traces of all three primary colours. For example Yellow Ochre is a greyed yellow so in addition to yellow it contains traces of blue and red (Yrb). Payne's grey is a greyed blue (Bry) and similarly contains all three primaries.

The conclusions from this when mixing colours are:

  • Bright colours will not be achieved by mixing colours which contain significant proportions of all three primaries e.g. Yr + Rb + Br, or YR(Orange) + Br etc.,
  • Neutral colours will be produced when similar proportions of all three primary colours are present.
  • Fairly Bright colours will be produced when only a trace of the third primary is present. e.g. Rb + Yr, or Yb + Ry etc.,
  • Bright colours will be produced when there are only two primaries present in a mix e.g. By + Yb, or Ry + Yr etc.
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