Color theory is an immensely complicated subject, and is understood differently by scientists, printers, web designers and painters. Subtractive color (where mixing the hues will create black) is what oil painters generally use, and some grasp of the theory will help you understand:
1. Why some colors 'work' together, and others don't.
2. How paintings are designed: color is a vital element of composition.
3. The principles that have guided successful painters, and which are still useful.
4. How to mix colors — if only very broadly: pigments have individual properties.
Colors are classified by three properties: hue, purity and value — terms that are often misunderstood. Experimenting with a graphics program will get the distinctions into your head, though colors mix differently on screen.
The intrinsic color; the wavelength of the light concerned. The strips shows primary, secondary and tertiary hues.
The freedom from other color admixtures. Saturation is the degree of purity. Chroma is the purity in relationship to gray. (N.B. Some authors also use intensity to mean color purity, whereas for others it means tone/value.)
The luminance — brightness or dullness — of a hue, as measured by the amount of light reflected. Also called tone or tonal value.
A tint is made by adding white to a hue, and shade is made by adding black. As far as oil painting pigments are concerned, mixing in white or black will usually lower the purity of a hue, making it chalkier or muddier.
primary & secondary
Red, yellow and blue are the primary colors, which can't be derived from still more basic colors. Mixing two primary colors will create one of the secondary colors: orange, green or purple. A secondary color mixed with an adjacent primary (on the color wheel) will create a tertiary color.
Colors are also commonly described as warm or cold. Warm colors lie at the orange-red end of the spectrum, and are 'active', causing them to 'advance'. Blue colors, particularly when dark and/or undersaturated, are 'cool' and tend to 'recede'. Other areas of the spectrum remain neutral.
Color theory provides a only rough guide only to mixing paints. In practice you will need to:
1. Experiment to learn the individual properties of pigments and their mixtures, probably making reference charts to begin with.
2. Make more attractive tints and shades with colors other than white and black (e.g. light and dark earths).
3. Purchase pigments for the secondary and certainly the tertiary colors. Mixing primaries will only result in muddy hues.
4. Use glazes if you wish to modify colors without mixing them overmuch.
As always, the important thing is to see for for yourself — to study the great masterworks and experiment with their color schemes to understand what has been done and why. You can do that easily today by taking copies of the work (scanning books or using Internet sites) and analyzing them with a cheap graphics program.
There are indeed many schemes for color harmony, but the following should be useful to the painter. Note that they apply only to hues: for variety you can (and should) vary the purity and tones of the hues concerned.
One hue. Composition is achieved entirely through adjusting purities and tones. A limited but powerful approach, that always makes a good exercise.
In this detail from his 'Diana and Callisto' (1556-9. National Gallery of Scotland. Edinburgh), Titian has used a simple orange hue throughout, not far from that shown above in the color purity strip. The marvelous variety comes from modifying purity and tone with glazes and scumbles — which demonstrates the power of old master techniques. (The whole picture uses a wider color range, including blue and a pink-red.)
Composition uses one hue and its complementary — e.g. blue and orange. The hues can be mixed in various proportions, and tones added with white or black (or preferably earth pigments).
The detail comes from a famous painting by Monet of the 'Beach at Trouville' (1870). It was painted on the spot. Though seeming a careless, even clumsy, improvisatory sketch, it is nothing of the sort. Monet served a traditional apprenticeship, and is here playing off an orange in beach and flesh tones against chalky tints of blue.
Composition using just 3 hues of 12-color wheel - e.g. orange, orange-red and red. As before, the hues can be mixed, and their tones adjusted.
This scheme can be further divided into:
1. one pure hue and the other two semi-neutral (i.e. mixed, muddy, low intensity). The pure tone will advance more than the others, whether is warm or cold.
2. high key pure hues. Usually applied in a broken fashion so that hues of the same value shimmer when seen close to, but group to broad areas of color from a distance.
3. one dominant, one subordinate and one minor. The dominant is varied with different purities and values.
The detail is from Eugene Delacroix's 'Death of Sardanapolis'. 1826. Musée du Louvre. Paris. The whole picture employs an analogous color scheme of red, red-orange and orange.
Like analogous, but with the addition of the complementary of the mid-hue of the analogous range. A warm/cool balance is more easily introduced with this scheme.
This intimate painting by Mary Cassatt ('The Bath'. c. 1892. The Art Institute of Chicago) uses tertiary hues, and falls somewhere between a triadic scheme and a split complementary one of red-purple against hues of green-blue. The background repeats the foreground colors but in muddier and darker colors.
Uses all three hues that are equidistance on color wheel. Hues may be varied in purity and tone as usual, and the scheme is further divided:
1. Primary colors only: very difficult to use outside posters and graphic design.
2. Secondary triadics, e.g. scarlet, mauve and viridian. Very beautiful effects can be achieved, probably because all colors contain some of the other two secondaries.
Green, blue and yellow appear in this detail from Vermeer's 'The Music Lesson' (c. 1664. HM The Queen's Royal Collection. St. James's Palace). Harmony has also been achieved by very skillful use of tone.
Harmony is also achieved by using colors of similar purity or tonal value. The harmony is not generally an expressive one, however, and is more useful to industrial and graphic designers.
All paintings have color, and will not be successful unless some color harmony scheme is articulated. You will need to:
1. select from the colors in the subject in front of you, or
2. emphasize certain aspects of the colors in front of you, or
3. impose a scheme of colors that does not occur in the subject
Some paintings will require a combination of all three strategies, but the implementation requires practice and a clear notion what you're trying to achieve.
You'll find the following useful:
1. Worqx Color. An excellent tutorial on color theory, providing an explanation of terms and effects, with illustrations from graphic design, advertising and website design. The select list of references will take you even further.
2. Artist's Real Color Wheel of Pigments. Site sells a color wheel ($10) and a complete color course on CD ($35) but also contains much free information on color and painting generally. Particularly useful is the color wheel which allows you to quickly find pigments to match a desired color. Also see color room theory
3. Color Wheel Pro. Software that lets you experiment with harmonious color combinations. Caters for all the common schemes, but shows hues only, not different purities or tones. $39.95. Free demo version.
4. 'Painter's Guide to Color 'by Stephen Quiller. Watson Guptill. 2000. Advice and palettes for most assignments. Aimed at the intermediate painter, and includes a color wheel.
5. 'The Color Compendium' by Hope and Walch. Van Norstrand Reinhold 1990. A good introduction, covering all aspects of color.
6. T'he Elements of Color' by Johannes Itten. Van Norstrand Reinhold. Aimed at artists but includes interesting psychological and optical information.
7.' Art Mixing Bible: All You'll Ever Need to Know About Mixing Pigments in Oil, Acrylic, Watercolor, Gouache, Soft Pastel, Pencil and Ink 'by Ian Sidaway. Watson-Guptill. 2002.
8. Color Matters. Basic principles of color harmony.
9. 'Eye and Brain' by Richard L. Gregory. Princeton Univ. Press, 1997.
10. 'Color Theory and Mixing'. Wet Canvas. 16-part lesson: free.
11. 'Vision and Art: The Biology of Seeing 'by Margaret Livingstone. Harry N. Abrams, 2002.
12. 'The Artist's Eyes: Vision and the History of Art' by Michael F. Marmor and James G. Ravin. Harry N. Abrams, 2009.
13. 'The Vision Revolution: How the Latest Research Overturns Everything We Thought We Knew About Human Vision' by Mark Changizi. BenBella Books, 2010.
14. 'Avoiding Muddy Colors'. John Morfis' helpful notes on Hello Artsy. June 2015.