For a bit now I have wanted to write about topics that aren’t specifically my designs or artwork. I don’t want to write about subjects that have nothing to do with art or design, though. I call this my portfolio, after all. It would indeed be interesting to have writings about design mixed in with my other compositions about my work. Color seems like as good a subject as any to write about as it is very important to both art and design. It is indeed a very detailed subject to write about and would take a few posts to cover; this one — the first one — should focus on just what color is.

Many artists are fond of saying they aren’t good at either math or science, but artists reading this are about to discover that color has a lot to do with both math and science; the color theory many of us were taught in art classes is based upon early 19th century and earlier perceptions of what color is and has little to do with the reality of it.


The Electromagnetic Spectrum A vertical diagram of the electromagnetic spectrum with the visible spectrum depicted as a small rainbow gradient. Gamma rays X rays Ultraviolet Infrared Microwaves Radio waves Long radio waves
The electromagnetic spectrum1

We are taught in science class that visible light is simply a small section of the electromagnetic radiation spectrum that we are capable of seeing. Color is our perception of visible light. See that pretty rainbow in the figure above? That really tiny rainbow is the entirety of our vision. Kind of depressing isn’t it? Some creatures like birds can see into the ultraviolet end of the spectrum and see that as additional colors we can only dream of viewing.

Human Vision

Our entire perception of color is based upon our own biology, our own ability to process color. We are trichromats, meaning we have three types of color receptors — cones — in our eyes. Contrary to popular belief we don’t have cones which are strictly sensitive to just red, green, and blue. They are actually sensitive to a range of wavelengths with peak sensitivity at neither red, green, nor blue. The way we actually see is quite a bit more complicated and interesting, but it is irrelevant to what I want to discuss here. Effectively what all this means is that what we see as visible wavelengths of light is entirely due to how our brains process the visual information from our eyes. The wavelength itself is what causes the color. For example light with a wavelength of 580 μm is perceived as yellow by our eyes. Long ago people discovered that you could create other colors of light by mixing red, green, and blue light. However, later when measuring the wavelengths necessary for each primary to mix each color of the spectrum they discovered that from just outside primary blue to primary green a negative amount of red was necessary to mix those colors. This means that not all colors we can see can be mixed by mixing red, green, and blue primaries. This also means that your computer displays which use an array of red, green, and blue subpixels to produce the images on your screen cannot replicate every color a human is capable of seeing.

CIE 1931 Color Space

In 1931 a lot of really clever people got together in Cambridge, United Kingdom. They had to develop a way around the negative red wavelength problem so they could create a color space that could represent every possible color. Their solution was to transform the numbers to where all values would become positive so they would be easier to work with, creating three imaginary channels called X, Y, and Z. This is a much simplified description of what occurred, but I don’t need to go into more detail on the subject. A color in that model is represented by three dimensions, meaning it can be graphed out in 3D space. The color spectrum itself being a series of colors was graphed out into 3D space, producing a plane. That isn’t the most useful way to visualize the data; it needed to be in 2D so it could be written on paper. If anyone remembers anything of what should be their high school mathematics the projection of a 3D plane to 2D can be done by simply dropping one of the axes. The Z channel in CIE 1931 XYZ is luminance which determines how intense a color is and isn’t important to mapping out the spectrum; they dropped that axis. The resultant graph looked something like this:

The CIE 1931 Color Space Chromaticity Diagram A chart depicting the entirety of human vision. Wavelengths of the colors in the spectrum, white points, and the extent of CIE’s standard RGB gamut are also displayed. x y 460 480 500 520 540 560 580 600 620 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
The CIE 1931 color space chromaticity diagram2

This doesn’t look much like the color wheel, does it? The curved line around the edge represents the spectrum, but at the bottom there is a straight line between blue and red which contains purples and magentas that aren’t in the spectrum; they are, however, colors we can see. Additionally there is a triangle drawn on the graph. This represents the standard CIE 1931 primaries. This is the area within the entirety of our color vision which can be mixed using red, green, and blue; anything outside that triangle cannot. Marking off the primaries is how we get the RGB color model. More on that later; but first, what is that curve and circle in the middle?


White light is entirely an illusion. There is no color white on the spectrum. White is simply a mixture of all wavelengths of visible light. The circle in the center of the diagram earlier is called equal energy which means it has equal energy across the spectrum, producing a true white. However, this isn’t really achievable. White light has a hue to it depending upon the change in its temperature. This is where color temperature and white balance comes into play. Anyone familiar with light bulbs knows that no bulb gives off pure white light; when we purchase them the color temperature is clearly stated on the packaging.

I began this essay by describing the visible spectrum’s placement in the electromagnetic radiation spectrum. Absolutely everything in existence that is above absolute zero — or 0 K — gives off radiation. We ourselves radiate in the form of infrared radiation — which is what we perceive as heat. If you were to set yourself on fire you would begin to glow. This is what occurs when the radiation given off by an object enters the visible spectrum. The waves of heat you see outside of the glow is infrared. If someone was an idiot and decided to put you out using alcohol you would in a blink of an eye glow from its original mostly-red color to bright yellow, yellow-white, very pale green-white, cyan-white, and lastly blue as the heat of the fire increased and you certainly died. The only comfort in your death comes from the scientific demonstration in color temperature it provided. We instinctively associate heat and fire with red, but red fire is colder than yellow or blue fire. This is completely backwards from our cultural perceptions of color where red is hot and blue is cold.

Temperature3 Source
20000 K Clear blue sky
10000 K HID xenon bulb
7504 K North sky daylight, Standard Illuminant D75
6504 K Noon daylight, Standard Illuminant D65
5503 K Mid morning/mid afternoon daylight, Standard Illuminant D55
5454 K Closest possible light to equal energy
5003 K Horizon light, Standard Illuminant D50
4150 K Moonlight, Standard Illuminant F6
3200 K Typical incandescent light bulb
2856 K Tungsten filament light bulbs, Standard Illuminant A
1850 K Candlelight
1000 K Embers

Daylight isn’t sunlight. Sunlight is direct light from the sun while daylight is direct sunlight and skylight mixed. For example shadows in the outdoors are blue because they are lit by the skylight and not the direct sunlight. Sunlight changes its color as the Earth rotates in relation to the sun. At sunrise and sunset sunlight has far more atmosphere to pass through which makes the light become cooler and toward the red end of the spectrum. Extra components such as smog and other particles in the air affect the color of the light as well, making it cooler in temperature. Fluorescents are often described as giving off an “unnatural light”. This is because fluorescents are lit from phosphors and not from heat; the light given off is missing many parts of the spectrum, and cheap fluorescent lights are often made to emit more light from the green end of the spectrum to make it appear brighter. That is why they appear green sometimes.

Why is this important? Because no white you see is colorless regardless of how it is emitted. The brightest white your computer screen is capable of producing isn’t pure white. There’s a hue to it which affects how all colors on the screen are displayed. This varies from device to device, so your digital artwork or design can look different to someone else viewing it on another screen. This is just like how a painting lit in a particular gallery can look different in another gallery lit a different way. Our perception of the color of an object is always affected by how it is lit or the color of objects around it. Our eyes and brains will filter and adapt to various light sources of differing temperatures. We must be aware of all of this when painting and designing.

I plan on writing more about color, discussing the color wheel, and eventually getting to gamut mapping and printing. Before I get there I would need to describe RGB, HSB, CMYK, and L*a*b*. I’ll do that next.

  1. This diagram is not to scale. The area of the spectrum visible by humans is so minuscule compared to the rest that just to get a single pixel of the visible spectrum would take far more than possible.
  2. This diagram is modified from its original source on Wikipedia. The colors shown within this diagram are only for visual guidance; they do not and cannot accurately represent the colors as a computer display cannot show them all.
  3. The colors in this table are only for visual guidance. The colors cannot accurately represent the true values as the computer display itself has its own white point.