Art Fundamentals No 1: Color Theory

I fully admit I have no formal training in art. I certainly appreciate that this is not some declaration of any innate talent; but, more that it is an acknowledgement that I have a great deficit in knowledge that impairs my ability to improve my skills.  Ask any artist and you are likely to get a variety of responses to “the fundamentals” albeit they tend to center around shape, form, values, anatomy, and color theory.  And its this latter one, color theory, that I want to spend a bit of time sharing what I’ve learned thus far, along with provide a bunch of resources (mostly online) that I think are worthy of further exploration.

It should be noted that while I am generally trying to get a practical understanding of color theory, inevitably there is a bit of a rabbit hole for which one can find one’s self going down.  While I personally find the deeper parts on the philosophy of color exceedingly important to build a strong mental model on the theory, arguably you do not need these underpinnings from a purely practical perspective on application.

Perception Trumps Physics

One of the most important things to appreciate in understanding color as an artist is that color is not absolute, but relative.  This is especially important to note for those with a science or physics background, such as myself, who may fall prey to thinking of color as purely a manifestation of wavelength of light.  While this is certainly true in context to the emission and absorption of electro-magnetic radiation, this level of understanding, if anything, largely obstructs us from better understanding how the human eye is stimulated by light that is then processed by our brains.  In this regard, the philosophy of color is more central to our pursuits than the science of light.  Like I said, the rabbit hole is never far, and once one stumbles into it it’s hard not to fall very deep indeed.

A generally accepted, albeit incorrect understanding of human vision, is that we see in three colors of blue, green, and red.  And that the brain processes this to create the infinite number of colors that we perceive.  While it is correct we have three types of cones, unfortunately, their labels oversimplify the reality.  These three types of cones actually perceive a spectrum of colors that largely overlap; but where they differ is where they are most sensitive within the color spectrum.  Interestingly, blue cones are the least common and do not exist inside the fovea centralis where both green and red cones are crammed.  It is important to note, again, that the cones are colloquially labeled for a single hue (or color), but in reality they are sensitive to very large spectral range with a significant overlap, especially for the red and green cones.  For the persnickety reader, these cones of red, green, and blue are often referred to as L, M, and S, respectively, by the academic literature, where the letters are references to the long, medium and short wavelengths of visible light.

Spectral absorption curves for the three cones – red, green and blue – of the human eye.

Now, we do not actually know how we perceive color, although they are of course theories such as the opponent processing theory which generally states that the signals from the 3 cones L, M, and S along with rods (brightness) are used to compute three differences, or: 1) quantity or brightness which is a combination of all cones and rods ; 2) amount of red-green; 3) amount of blue-yellow.   This theory handily explains why humans cannot perceive a yellowish-blue or a greenish-red, since in opponent processing theory these colors work into opposition to each other to create a single value, as it were, that is used to process color.

It is particularly important to remember that for any given wavelength of the EM spectrum it does not have, as an intrinsic quality, color.  Color is fundamentally a quality of human perception.  Human perception of color works through a subtractive process noted above by the opponent processing theory, so whereas a physical understanding of light (not color) is arranged as a linear spectrum with longer wavelengths such as “red” to one side, and shorter wavelengths such as “blue” on the other end, the human perception of color is better modeled as a circular spectrum where colors are next to their neighbors in a harmonious, blended manner with complimentary colors always opposite to each other.

Color Wheels

Simplified color wheel showing RYB as primary colors. Note, traditionally artists used RYB as their primary colors; however, as our understanding of human perception improved RGB was introduced to better represent human perception of color. Regardless of RYB vs RGB, general concepts of primary and secondary colors continue to apply to both.

The concept, generally speaking, behind a color wheel is that you can start with the three primary colors – in the case of above we show red, yellow and blue – and subsequently add them in varying proportions to get other colors on the wheel.  In the above, if we combine blue and yellow we get green.  And blue and red produce purple.  And so on and so forth.  Note, the above color wheel greatly simplifies matters as its ignores variations of saturation and value.

Relationship of Hue, Chroma and Value

While we often think of “red” as a color, it is more accurate to consider “red” a component of color.  More specifically, color is generally accepted to be broken into three major attributes, or

  1. hue – the family of color such as red, blue, yellow, et cetera
  2. chroma – the intensity or saturation of the color
  3. value – the amount of lightness, or white or absence thereof

Why is this important?  While a color wheel is a very practical tool, it occludes from an artist the importance of value, and more in particular, how not all hues are created equal in this regard to value.  This is where Munsell color system can provide some insights, even if we opt to not adopt the nomenclature proposed by Munsell.

Munsell color system depicting hue, chroma and value in three dimensions.

Munsell’s color system helps to take those three above attributes, and depicts them in three dimensions.  Munsell is not the first to connect these three attributes into three dimensional space, but he is the one who best pursued this to create a system that most closely matches what the human eye can perceive.

One might think of these 3 attributes defining a sphere, or an apple, since along the central core going top to bottom is are the values.  In Munsell color system, everything was meant to have well defined values such that any color can be accurately described by its coordinates in this three-dimensional space.  Looking from the top down on this core working radially around are the hues such as red, yellow-red, yellow, green-yellow, et cetera.  Finally, working outward from the core along any defined hue is the chroma, or intensity of the hue for a given value.  While both hue and value are constrained between a range, chroma is not.  In theory, chroma extends out to infinity.

Now, while that is all very interesting, the real insight comes from the fact that the sphere is not a smooth sphere at all.  The below is a vertical slice of the Munsell sphere between hue 5Y (yellow) and 5PB (purple-blue).  What I want you to pay particular attention to is how the for any given value, the amount of chroma (intensity of color) varies for both hues.  I would argue that the most intense purple-blue happens around chroma of 12 and value of 5.  But for the yellow, it s actually at chroma of 10 and value of 8.  Why is this important?   This is critically important, especially if as an artist you start with values to block in shape and form first, and then use overlays of color.  Because the values you pick will implicitly determine what colors you can subsequently overlay.

12 10 8 6 4 2 0 2 4 6 8 10 12
255 255 255
228 228 250
232 232 232
243 227 207
250 227 178
190 201 239
200 200 222
203 203 203
215 200 181
221 200 154
227 200 126
233 199 97
237 199 63
142 176 241
154 175 225
164 175 210
173 174 195
179 179 179
188 173 155
194 173 128
200 173 101
205 172 72
210 172 29
79 150 244
101 150 227
116 149 213
128 149 198
138 148 182
146 148 168
150 150 150
161 147 129
167 147 103
173 146 75
178 146 42
46 124 214
72 123 199
89 123 185
101 123 171
111 122 156
120 122 142
124 124 124
134 121 103
141 121 77
146 120 48
150 119 9
38 97 172
59 97 158
74 97 144
85 96 130
93 96 116
97 97 97
108 96 77
114 95 52
119 94 25
26 72 133
45 72 120
58 72 106
67 72 92
70 70 70
81 71 55
87 70 33
20 49 93
35 49 79
44 49 66
48 48 48
57 48 34
63 47 6
1 5PB
13 28 56
23 28 45
28 28 28
37 27 9
0 0 0

This is well illustrated by Sycra with one of his YouTube videos where he clearly demonstrates how the process of value to color is interlinked.  To wit, it is critically important to understand this relationship otherwise your application of colors will result in muddied, muted colors or otherwise otherworldly colors that do not land well.

Primary and Secondary Colors

There is nothing specifically special about primary colors.  Well, there is, but that is only when you are trying to increase the number of unique colors that can be perceived, but we will discuss this in a bit under gamut.

The concept of primary colors, and in particular, the three primary colors that we are taught of red, green, and blue (RGB) are purely an artifact of the study  of human perception and those three cones (L, M, S) we mentioned previously.  We will ignore additive vs subtractive process differences for now, but just note that colors are added together when combining light such as your monitor, but colors are subtracted when other mediums such as printing and painting are involved.  That said, the primary colors of RGB are for additive processes, whereas CMYK (cyan, magenta, yellow, and black) are for subtractive processes.

That all said, the combination of the primary colors create secondary colors which are purely defined as colors created when two of the primary colors are combined in equal proportions.  And the combination of the primary and all subsequent colors effectively result in those primary color’s color gamut.

Complimentary Colors

Complimentary colors are simply colors that are on opposite sides of each other in a color wheel.  Generally speaking, at least for the RGB color wheel, complimentary colors have the largest perceived contrast to each other.  Thus, one can argue orange is used for outdoor where as it provides the greatest contrast against greens and blues such as trees, skies and water.  And more so, complimentary colors are aesetically pleasing to the majority of humans.  Whenever considering your color scheme for a picture, one simple approach is to big one color to be the primary color, and its compliment to be the second color.

This picture uses two colors primarily for its color scheme, or gamut, that are generally complimentary in nature. Orange-red with green-blue.

Color Gamut

But what is a color gamut?  Simply put, it is the color space or all the color combinations that can produced by combining colors first starting with the primary colors.

Again, as we emphasized above, color itself is purely a quality of the human brain’s ability to perceive different combinations of light with differing wavelengths and intensity.  Color itself is not a quality of the light itself.  So this why we say that there is nothing particular special about the primary colors in and of themselves.  They are selected for a singular purpose: to produce as many possible permutations of color that the eye can perceive.  If you selected three different colors arbitrarily you’d be able to create a color wheel, but you would discover that some of the colors from the RGB color wheel just could not be reproduce.

So RGB are our primary colors for the sole reason that they yield the largest color space, or color gamut, tuned specifically to the human eye.  Pick a different set of primary colors and you get a different gamut.  And this, folks, is why when working digitally it is so important to know your color space.  Since different color spaces do not entirely map onto each other; colors that can be represented in one gamut simply do not exist in another gamut.  This is particularly acute when transitioning from display color space, which is typically RGB, to print’s, which is nominally CMYK.

Various color gamuts for both display and print.

Note how different color gamuts only generally overlap.  In particular, whereas RGB has the largest gamut albeit still not sufficient to reproduce all the colors that the human eye can perceive, it is significantly better than print such CMYK.  Given how much smaller CMYK is to RGB, it is very important when creating artwork that will be printed to understand this and ensure that you work within the correct color gamut for the intended output, otherwise you will sorely disappointed in your results; this no more so than when comparing the differences of your artwork on your computer screen to its output on a printer.

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