Color responses are more tied to mans emotions than to his intellect. In general, people do not respond to color with their minds.

—Deborah Sharpe

Of all the senses that connect us to the world—vision, hearing, taste, smell, and touch—vision plays by far the largest role. More than 80 percent of our sensory experiences are visual. We are drawn to light, and to color. The instrument used in solving color problems in the design studio is the unaided human eye. For artists and designers, dyers and house painters, printers and carpet sellers, even when aided by tools of color technology, final decisions about color are made by human eyes alone.

The Sensation of Color

The experience of color begins with a sensation. A sensation is an actual, physical event. It is the body's response to a stimulus, something that is encountered from the outside world. Light, which is visible energy, is the stimulus for the sensation of sight. That stimulus is measurable: the color and quantity of light emitted by a light source can be measured. Sensations are also measurable. An individual's ability to detect light is measured as visual acuity, or sharpness of vision. Visual acuity is the ability to sense patterns of light and dark and to resolve detail. It is a measure of the weakest light stimulus that an individual can detect.

Threshold

The threshold of vision is the point at which an individual can no longer detect a difference between two close samples.

The ability to see differences between dark and light is not the same as visual acuity for color. Someone who can discriminate very small differences between a dark gray and a slightly lighter one may not be able to detect a difference between two reds, one of which is slightly closer to orange than the other.

Visual acuity for color is the ability to detect differences between wavelengths (colors) of light. Although the strength and wavelength of each color of light can be measured with scientific instruments, human beings do not see the spectrum as a series of separate colors. The spectrum of light is sensed as flowing and unbroken, with each color blending into the next.

Color vision enables a viewer to discriminate differences between hues in this continuous band, like the difference between a red and a red-orange, or a blue and a blue-violet. An average human eye can discriminate about 150 steps, or individual colors (hues) of light. It makes no difference whether the colors are seen as direct light or as light reflected from a surface. This number does not include the darker, lighter, or duller variations of each hue. Between the 150 hues and their many variations, a person with normal color vision can distinguish millions of different colors.

The threshold of color vision is the point at which a difference between two similar hues can no longer be discriminated. Individuals with normal color vision vary in the threshold of color acuity just as much as they do in their ability to see detail. Each person's vision is modified by factors like individual physiology, health, and age. Infants are believed to be able to detect differences between dark and light before they can see hue, and many older people experience a progressive deterioration in their ability to discriminate between blues, greens, and violets, caused by a gradual yellowing of the lens of the eye over time.

Intervals

One way to characterize differences between color samples is in intervals. An interval is a step of change between visual sensations. An individual's threshold establishes the single interval: the point at which a detectable step can no longer be inserted between two close colors. Single intervals take concentrated effort to see and are tiring, but they play a role in many special effects and illusions.

Parent-descendant color mixtures are a basic interval relationship. They are illustrated as three colors arranged in a linear series, with a “parent” at each end and a “descendant,” the step between them, in the middle. Parent-descendant color mixtures play an important role in color harmony and are also the basis of many special effects and illusions.

Even intervals occur when the middle step is visually equidistant between the two parents. Some representative sets of even intervals are black on one side, white on the other, and middle gray between them, or red on one side, yellow on the other, and orange between them. The important thing about even intervals is that the midpoint be just that: no more like one parent than the other.

Parent-descendant mixtures can be set up between colors having only hue difference, like red and blue; only value difference, like black and white; or only difference in saturation, like brilliant blue and gray-blue. Intervals can also be set up between color samples that contrast in more than one quality. A brilliant yellow-orange and a tint of muted violet have hue, value, and saturation contrast, but a middle step can still be found between them.

Intervals are not limited to the three steps of parent-descendant color mixtures. In a series of even intervals, each step is the visual midpoint between the samples on either side of it.

Parent-descendant color mixtures occur so frequently in color study that the word “interval” alone is often used to mean an equidistant step, but intervals can also be uneven. Tilting a middle color closer to one parent than the other can be a deliberate choice, particularly in illustration.

Creating order out of random information is a fundamental function of human intelligence. Things are categorized in order to control and understand the flow of information: large to small, A to Z, ascending numbers, dates, or sizes. Orderly information is easier for the brain to process; haphazard information is more difficult. Even intervals are orderly. They are easy for the eye and brain to process. Images composed of even intervals are more quickly and easily understood than images in which intervals are uneven or random.

Even intervals are visually logical mixes. They are judged by eye alone. Members of a group rarely arrive at complete agreement as to the exact midpoint between two samples. The disagreement is about nuance, not about great differences, and can be attributed to individual differences in visual acuity and interpretation. A perfect interval, like perfect weather, is an opinion that includes a generous helping of fact.

A gradient is a series of progressive intervals so close that individual steps cannot be discriminated. It is a seamless transition between differences, whether from light to dark, or from one hue to another, or from a brilliant color to a dull one. Shading, for example, is a gradient of values, a wash of color from dark to light.

The Perception of Color

A sensation alone—a touch, taste, smell, sight, or sound—is an incomplete event. The occurrence of a sensation is followed immediately by perception. Perception is the critical connection between human beings and their environment. It is cognitive, or “knowing”—the understanding and awareness of what has been sensed. Perception recognizes and identifies the sensation. It decides what has been sensed. Perception acts as a filter, separating useful and important information from competing stimuli in the environment.

When the brain receives a light stimulus it first interprets form as distinct from background by sensing patterns of light and dark. Figure-ground separation, or pattern recognition, is the first cognitive step in the process of perception. It identifies situations by forms and their arrangement.

Color plays an important, but secondary, role in recognition. A red file folder (unpaid bills) and a blue file folder (paid bills) seem at first to be identified by color. But both red and blue folders are identified first as file folders, and only secondly by color. The initial recognition is of form: this is a file folder, not a notepad, not a CD, not a book.

Recognition is based on learned information from a multitude of sources: individual experience, social and cultural traditions, environmental surroundings, formal teaching. The ability to recognize sensations develops with astonishing rapidity, beginning almost at birth. By adulthood human beings have acquired and stored an immense database of recognized sensations. Everything seen is understood because its identity has been learned and the experience of it held in memory. New sensations, unless they are accompanied by additional information, are identified by referring to this stored information. Something new is recognized, correctly or incorrectly, because it is associated with some familiar thing that has similar characteristics.

Most perceptions occur unconsciously and at such high speed that they seem simultaneous with sensation.¹ The experience of color is always a fusion of sensation and perception. Unlike a sensation, a perception cannot be measured. It can only be described. Understanding how we see, and how we process and respond to what we see, translates directly into design applications. A working knowledge of the fundamentals of perception provides information that helps the designer to direct, even at times to control, the way a design will be received by its target audience.

Physiology studies the body and its functioning. It is a measurable science that can quantify the body's physical responses to a stimulus of color. Psychology studies behavior; or how organisms perceive and react to situations when they are stimulated in different ways. Psychology can describe—but cannot precisely measure—the ways in which human beings recognize, interpret, and respond to a stimulus of color. Psychology deals with perception.

Physiology: Responding to Light

The nervous system is an information pathway from the outside world to the brain. It is made up of three kinds of cells: receptor cells, transmitter cells, and brain cells. Receptor cells receive information from the outside world (stimuli) and change it into a form of electrical energy that the brain can use. Transmitter cells carry these signals to the brain. Signals from each sense are received in separate, specific locations in the brain. The brain decodes each sensory event first by identifying which sense has been stimulated, then discriminating specific qualities within that sense. In music, for example, it discriminates between notes; in vision, red from blue. Processing the information and generating a response is the final step.

The eye is the sense organ that detects light. Light enters the eye through the pupil and falls on the retina, the inside back of the eye. The retina is made up of two kinds of light-sensitive receptor cells, rods and cones. Both rods and cones connect to the optic nerve, which transmits the sensory message to the brain.

Rods and cones respond selectively to available light. Cones dominate vision when a good deal of light is present. Cones are responsible for color vision and for the ability to see detail. Objects appear more colorful and fine detail, like small print, is clearer when cones are dominant. Rods dominate vision in low light. Rods are responsible for peripheral (surrounding, less focused) vision. Colors appear muted and fine detail is more difficult to see when rods dominate.

The visual field is the extent of area that can be seen by the two eyes of a viewer standing in one position. The fovea is a tiny area at the back of the eye that is the center of the visual field. The fovea contains only cones. It is the most sensitive area of the retina, detecting patterns of light and dark and color with the greatest clarity. Images and colors are seen less clearly when the light stimulus moves away from the fovea.

Adaptation is an involuntary response of the eye to the quantity of available light. Both rods and cones are always at work. The retina moves back and forth (adapts) quickly between rod and cone dominance as the amount of available light changes. Objects appear more colorful at higher lighting levels, when cones dominate. Color perception lessens in dim light when rods dominate; perception in low light is in shades of gray. A garden that is colorful by day loses its color gradually toward evening, but the contrast of dark foliage and light flowers persists as a different, but equally pleasing, image. Adaptation takes place under any lighting conditions. “Cones for color, rods for gray tones” is true for objects seen under sunlight or gaslight, fluorescent, LED, halogen, or any other kind of light. The sly old metaphor is literally true: all cats really are gray in the dark.

Lateral inhibition is an aspect of vision that increases the eye's ability to distinguish edges. When a pattern of light/dark contrast reaches the retina, the cells that receive the light part of the image inhibit the ability of the ones next to them to detect light. As a result, areas next to bright spots appear darker. The greater the quantity of light, the more lateral inhibition takes place: light areas appear lighter and dark areas darker.

The sensation of light is received in two areas of the brain: the cerebral cortex and the hypothalamus, or midbrain. The cerebral cortex is the center of cognitive activity. It receives information and processes it, recognizing, interpreting, and structuring a response to each stimulus. The midbrain controls the internal environment of the body. Sensations of light transmitted to the midbrain act as a biological stimulus to the central nervous system. The midbrain contains the center for regulation of blood pressure and body temperature. It also stimulates glands that control the production and release of hormones. When the brain is stimulated by a thought, mental image, or outside stimulus (like light), the midbrain triggers the release of hormones. A color stimulus can affect the strongest human needs and emotions—fear, joy, hunger, thirst, and sex.

The human body is adapted to function at a normal level in response to sunlight, to the sun's pattern of energy emission. Changing the strength of a color stimulus causes a change in the body. Exposure to an elevated level of red stimulates hormone production and raises blood pressure; exposure to an elevated level of blue has been shown to lower blood pressure and depress hormonal secretions.

The immediate biologic response of the body to a stimulus is phasic arousal. Phasic arousal is abrupt and lasts very briefly, like the surge of adrenalin that is experienced in a sudden and frightening situation. Phasic arousal requires a stimulus. Tonic arousal is the body's response over a prolonged period. The body has a norm for tonic arousal, and the brain continually directs the adjustment of hormone levels to keep it at that norm. Stimulation by a strong color causes phasic arousal—an immediate reaction—that can be physiologically measured, but the arousal is short term; the duration of the effect is not continuous.

Because exposure to color changes the body's hormonal balance, it can also modify emotional response and behavior. Colors can be chosen to stimulate, depress, or otherwise alter mood. In environmental design, overstimulation and understimulation have equally negative effects: human beings respond best to living spaces that have color, but not an overload of highly stimulating color. Restaurant designers use red, in its many variations, to stimulate the appetite. The muted colors of funeral homes are carefully selected to minimize emotional response.

An extreme example of color used to modify behavior occurs with a color known as Baker-Miller pink (a bubble-gum pink). It has been hypothesized that exposure to Baker-Miller pink reduces aggressive behavior. The effects are said to begin after a short period of exposure and last about for about half an hour—a perfect demonstration of the body's arousal pattern. Some police stations have rooms painted entirely in this color; there even are garments marketed in Baker-Miller pink that promise “to chill you out.”²

Colors can also be experienced without a stimulus of light. The brain alone, without a light stimulus, allows us to dream in color, or to imagine color with closed eyes. A headache or a blow on the head can trigger vivid images of blue stars. Color can be seen in the mind's eye.

Healing and Color

The eye is not the only organ that responds to light. Light is also absorbed through the skin. The use of colored light to act on the body through the skin is a routine medical practice. The treatment of jaundiced infants with light is a standard (and effective) therapy, as is the treatment of psoriasis, a skin disease, by exposure to sunlight.

The use of color to heal has a long history. Ancient color therapies included (among other treatments) the application of colored substances to the skin. Some were helpful, but not because of their color. They were effective because the applied substance had medicinal properties.

Color therapy remains an active field of study. Most contemporary color therapists ascribe healing properties to different wavelengths, rather than to colored substances. Certain colors of light are thought to have affinities to different parts of the body. The medical establishment is skeptical of these claims, and the practice of medicine by color therapists is illegal in the United States.

Synaesthesia

Synaesthesia is a long-recognized but largely unexplained phenomenon in which one sense responds to the stimulation of another. There are reports of blind persons (and others) who are able to determine the color of objects through touch. An experiment conducted by Charles Spence, a professor of experimental psychology at Oxford University, found that subjects reported a strawberry flavored mousse to be 10 percent sweeter when served from a white container than from a black one.³ A woman reports a humming sound when she enters a certain red room; the sound stops as soon as she leaves the room. A man reports a strong taste of lemon when he listens to a particular piece of music. Research indicates that the sensory pathways to the brain are connected to each other in ways that can be demonstrated but are not yet understood. The idea that undiscovered connections exist between the senses seems less surprising when we remember what an ordinary thing it is to experience chills—ordinarily a reaction of the skin to change in temperature—from an emotional, musical, or visual experience.

Psychology: Responding to Light

Visual acuity for color, hormonal responses to color, adaptation, lateral inhibition, and synaesthesia are involuntary biological responses of the body to a stimulus of light. The perception of color also includes involuntary psychological responses. The cerebral cortex, the reasoning part of the brain, identifies and organizes a response to each color stimulus that is unconscious but based on past learning. Stored information has a powerful influence on color perception. When Deborah Sharpe states that “color responses are more tied to man's emotions than to his intellect,”⁴ the underlying message is that color responses are shaped by experiences and associations that are long-buried in memory. Aunt Agatha made you eat broccoli in her pink kitchen. You have visceral, and very negative, feelings about broccoli and pink.

Another of these responses is a kind of expectation called memory color. Memory color means that the viewer makes an unconscious assumption about the color of something, the “orange” of an orange, for example. A viewer influenced by memory color does not report the actual color experience. Instead, what is reported (or even illustrated) is a preconceived idea. A still-ripening apple may be more green than red, but it will be described as red. At times the sea can seem nearly maroon; even so an unthinking—or unseeing—artist will paint it as blue.

Memory color affects the perception of objects of familiar coloration. Color constancy is a second and equally powerful form of expectation. Color constancy means that the colors of familiar objects retain their identity no matter what the general lighting. The eye and brain together adapt to all general light sources as if they were the same. Colors seen in a daylit room may undergo dramatic changes under man-made lighting, but the differences are unremarked. An image stored in memory overrides what is actually seen.

A second kind of color constancy occurs when close colors are perceived as being identical. In an all-white kitchen, the white of the refrigerator, the counters, the floor, the cabinets, and the paint may all be different, but the immediate cumulative effect is that they are the same. The various surfaces are categorized mentally as “white,” and the concept of “whiteness” prevails over the differences that actually exist.

In some circumstances it is appropriate to look for fractional differences between colors—in a design situation, for example—but a constant concern with small color differences would be exhausting as part of everyday life. Memory color and color constancy screen out important color differences from ones that do not matter. Because they simplify and edit what is seen, they play a large and useful role in the visual comfort of living with color.

Naming Colors

Color is recognized universally as a particular kind of visual experience. When the brain receives color information, it is identified by name. In a widely accepted study, researchers Brent Berlin and Paul Kay determined that ninety-eight languages had names for eleven basic colors. Simpler languages had fewer color names; more complex languages had more names. The languages studied gave names to colors in a consistent order of recognition: first, black and white (or dark and light), then red, followed by yellow and/or green, then blue, brown, orange, purple, and pink.

Only external evidence tells us that most people see the same thing when they see “red.” We accept that something is red not by scientific measurement but by unspoken agreement, common language, and common experience. Green leaves are identified in each language as green, not as orange. Disagreements that arise about the names of colors are about subtle differences, not broad categories. Something that is called red is simply more red than it is anything else. It may be a bluer red or a yellower red, but no one would ever call it blue or yellow.

Just as no one can know precisely what another person sees, no one can experience anyone else's idea about a color. Each individual holds in memory a personal picture for the meaning of each color name. Josef Albers observed, “If one says ‘Red' (the name of a color) and there are 50 people listening, it can be expected that there will be 50 reds in their minds. And one can be sure that all of these reds will be very different.”⁵ There are hundreds of different reds, and a surprising number of people assume that there is a fixed name for each and every one. If members of a group are asked to describe a red object by its color name, the answers are more likely to be “fire-engine red,” “cherry red,” or “lipstick red” than simply “red.”

Color study requires only six names for colors: red, orange, yellow, green, blue, and violet. Each name represents a family of closely related hues. Restricting the names for colors to six words enables the observer to focus on the visual experience. Marketing professionals use (and need) romantic names for colors, like Venetian Red, Bermuda Blue, or Aztec Gold because the images that these words evoke play a role in sales appeal. Both ways of naming colors are important as long as the critical difference between the two is recognized: the six hues of color study and their darker, lighter, and muted variants deal with eye training, color recognition, and color use; the countless color names of marketing are about product imagery and sales.

Color As Language: From Name to Meaning

Language is a collection of spoken words that convey ideas and feelings. Each word has the same meaning for those who speak the same language, although single words can have slightly different meanings for different groups of speakers. An American who orders “today's pudding” from a London menu, for example, may be surprised to be served a slice of chocolate cake. Writing is visible language. It is a visual code for speech and a means of preserving words and ideas. It is also a way of organizing and controlling the way that words and ideas are presented.

Dead languages are frozen in time. The meanings of words do not change. Living languages are continually evolving. The meanings of words in a living language change over time, or are lost entirely, or are replaced by new ones. Color, too, can be a language. Colors, or color combinations, can be visual codes that communicate ideas and feelings. Colors can influence the way ideas are presented. And like words, the meanings of colors can change, or be lost, or be replaced by new meanings over time. Color is a living language.

For every individual the meaning of a color, or group of colors, is shaped by a hierarchy of outside forces: culture, spoken language, social status, setting, time, and individual life experience. Semantics is the study of the meaning of words and the variety of their uses in language, including the language of color.

Culture is the social structure that establishes what is important to a group for people. Awareness of cultural differences in the semantics of color is critical to the successful marketing of any product or image destined for the global market. Sometimes a color is only a color, but many, many times it is more. In Color, Environment, and Human Response, Frank H. Mahnke describes the experience of color as a pyramid with six levels of response:⁶

personal relationship

influence of fashions, styles, and trends

cultural influences and mannerisms

conscious symbolism-association

collective unconscious

biological reactions to a color stimulus

Each step upward in Mahnke's pyramid represents a narrower interpretation of a color experience. The lowest level is the innate, unlearned response to color that is universal: the physiological response to a stimulus of light and its effects on the midbrain. The cognitive part of the brain becomes a part of the response at the second level, where each sensation is identified by name. “Collective unconscious” responses, like the association of the color red (and also the word for red) with blood, are also involuntary and cross-cultural.

At the third level colors become a language that is independent of words. Colors or color groups are used as symbols, or visual codes, for noncolor ideas that have formalized meanings for specific populations. Americans who see “red, white, and blue” interpret it as having some association with the United States. That the French and Chilean and flags (among others) employ the same colors has no symbolic meaning to an American.

Colors or color groups that symbolize major societal concerns like nationhood, death, and marriage tend to maintain their meaning over long periods of time. These color symbols can be thought of as permanent for each population. Traditional colors of mourning, for example—black in the West and white in India —are meanings unlikely to change. “The East Is Red” is both an anthem and a symbol of long-term political reality for communist China. The colors green and orange persist as symbolic of religious and political division in Ireland, present reminders of past conflict.

Color symbols of lesser social importance tend to be less stable in meaning. Just as words change in meaning, often in politically and socially potent ways, so do the meanings of colors. A symbolic color is sensitive to its time as well as to its audience. The Green Party, founded in Europe in the late 1970s, was perceived initially by many as a radical group bent on the destruction of modern society. Alliances of the Green Party with communist and socialist groups, known as Red-Green alliances, were viewed as threatening to social stability. In the twenty-first century, with global warming and the deterioration of the environment everywhere apparent, green has not only lost any negative political meaning in the West, it has become an international rallying color of environmental politics and a powerful tool for advertisers. “Green” products carry the implicit message that using them will help to save the world.

But even with the same audience and within the same time period, no color symbol is limited to a single meaning. Colors are understood as codes for ideas only when they make sense in context. Colors may inform, but they do not define a situation. Additional information is needed. The young woman in a long white dress may be a bride—or just a pretty young woman wearing a summer dress. The green that represents environmental concern in one setting implies youth and inexperience in another. Shakespeare's aging Cleopatra speaks of her “salad days,” when she was “green in judgment.” New recruits are said to be green. At sea, one turns green from seasickness, in another circumstance, green with envy. Green, the color of Ireland, the “Emerald Isle,” is also the color of Islam. And who can tell at a single glance if an orange and black scarf celebrates Halloween—or Princeton?

Some colors have become so important in communicating ideas that their meanings have been legislated. Color coding plays a central role in conveying safety information for many vigilance tasks, or situations that call for immediate response. The federally mandated OSHA⁷ colors used in the United States, and in many instances internationally, communicate physical hazards and safety information. OSHA yellow indicates caution; orange, dangerous machinery or equipment; violet warns of radiation hazard. Red indicates firefighting equipment and is recognized worldwide as an indicator of danger—red says “STOP.” Green indicates safety, or safety equipment. Safety colors and the situations in which they appear are closely linked in memory and processed very rapidly. An OSHA yellow rain slicker helps to protect the traffic policeman. The same yellow as paint on a chair suggests nothing about safety at all.

When colors are seen with simultaneous and conflicting information, the areas of the brain that respond to color compete with other parts of the brain in structuring a response. The resulting delay and confusion in perception, called Stroop interaction, takes place because the relative importance of equal and competing streams of information must be sorted out.⁸ The word BLUE written in RED causes a brief hesitation in the flow of reading. An octagonal green traffic sign that said “STOP” would be misperceived—and delay response—with potentially fatal results.

Impressional Color

Impressional or associative colors evoke imagery without further meaning. Grayed blues may call to mind the icy cold of a winter sea, and a riot of brilliant greens a tropical forest. Steel gray suggests hi-tech, soft pastels a new baby. Even a slight shift in any quality will alter an association. Yellow tilted to orange may suggest warmth and richness, but yellow tilted to green suggests illness. Red is associated with passion of all kinds: “There are reds that are triumphal and there are reds which assassinate.”⁹ The images brought to mind by a brilliant red will be different from those of a deep burgundy: the first the hot flame of Bizet's Carmen, the second the smoldering rage of Shakespeare's Iago.

Color As Words Alone

Written and spoken words for colors communicate the same symbolic ideas as actual colors but are understood more indirectly. Words are processed as thought rather than as sensory experience. The immediacy of a color symbol lessens when it is presented as words. Its meaning is unchanged. Reading the words “red, white, and blue” takes longer to process than the sight of an American flag in full color.

Color words used as metaphors are constant in writing of all kinds. A colorful personality is understood to be vital and interesting; a gray individual, not at all. No one has written more comprehensively, or with more eloquence and scholarship, on the imagery and symbolism of colors than Alexander Theroux:

Cranberry red has a saucy sharpness to it, with a hint of yellow. Bluish red, popular in lipsticks, cardigans, and the aura of dramatic personalities.”¹⁰

Does anyone doubt that celebrities have a bluish red aura? Theroux says it all.