Munsell Color Theory

For some time I have tried to find a starting point for discussions about colour theory. I have tried to do this for two separate, but related, reasons. Firstly, we talk about this at intervals during the online media degree course. Secondly, I need to write something authoritative about colour theory for the forthcoming Nobanet e-learning course.

Most of the material that I have found so far seeks to develop pseudo-mystical explanations for the feelings that we feel looking at different colours. This includes analyses such as this, from Smashing Magazine’s series on Color Theory for Designers

Warm colors include red, orange, and yellow, and variations of those three colors. These are the colors of fire, of fall leaves, and of sunsets and sunrises, and are generally energizing, passionate, and positive.

Finally I remembered a reference from some research I did while I worked with Mediumwave in the 1980s. I remembered the name Albert Munsell who, once upon a time, wrote a book called A Color Notation.

I looked him up and discovered that the system I remembered had become a recognised global system for categorising colors, and that it has become an official tool for recognising acceptable colours for “color branding; classifying soils, rocks and artifacts; grading produce; specifying color based on government standards; learning how color works; and more”, according to the Munsell.com site.

A quick look at Wikipedia tells us that the system measures colours according to Hue, Value and Chroma, defined as follows

Hue
Each horizontal circle Munsell divided into five principal hues: Red, Yellow, Green, Blue, and Purple, along with 5 intermediate hues (e.g., YR) halfway between adjacent principal hues. Each of these 10 steps, with the named hue given number 5, is then broken into 10 sub-steps, so that 100 hues are given integer values. In practice, color charts conventionally specify 40 hues, in increments of 2.5, progressing as for example 10R to 2.5YR.
Two colors of equal value and chroma, on opposite sides of a hue circle, are complementary colors, and mix additively to the neutral gray of the same value. The diagram below shows 40 evenly spaced Munsell hues, with complements vertically aligned.

Value
Value, or lightness, varies vertically along the color solid, from black (value 0) at the bottom, to white (value 10) at the top. Neutral grays lie along the vertical axis between black and white.
Several color solids before Munsell’s plotted luminosity from black on the bottom to white on the top, with a gray gradient between them, but these systems neglected to keep perceptual lightness constant across horizontal slices. Instead, they plotted fully saturated yellow (light), and fully saturated blue and purple (dark) along the equator.

Chroma
Chroma, measured radially from the center of each slice, represents the “purity” of a color (related to saturation), with lower chroma being less pure (more washed out, as in pastels. Note that there is no intrinsic upper limit to chroma. Different areas of the color space have different maximal chroma coordinates. For instance light yellow colors have considerably more potential chroma than light purples, due to the nature of the eye and the physics of color stimuli. This led to a wide range of possible chroma levels—up to the high 30s for some hue–value combinations (though it is difficult or impossible to make physical objects in colors of such high chromas, and they cannot be reproduced on current computer displays). Vivid solid colors are in the range of approximately 8.

These give a wide range of interesting diagrams in both two and three dimensions, which you can see at Wikipedia.

Update: finnish french fries

On November 29, 2017, at YLE’s English online news site I learned that the EU will issue a Munsell color chart for restaurants to use to measure the acceptibility of their french fries. YLE explains that

The EU has introduced a new regulation requiring food business operators to only serve customers chips – often known as French fries – that are a golden yellow colour.

Fries aren’t the only food item coming under closer scrutiny in Brussels. Officials will also be looking at other foodstuffs such as crisps, crackers, pastries, breakfast cereals, baby biscuits, cereals and jar food and bread in an effort to ensure that they do not contain acrylamide, a food contaminant that is considered a chemical hazard in the food chain.
Acrylamides typically form when starchy foods are subjected to high temperatures during cooking, such as baking, deep-frying and roasting. The substance is believed to be linked to the risk of cancer in humans…

Manufacturers of French fries will have to perform colour tests on cooked foods, using a Munsell food colour chart for comparison.

Now we see it: colour theory in action, as precisely calibrated “golden brown fries” save us from cancer!