What is a color?
A color can only be described in terms of a person’s report of his or her perceptions.
The visual spectrum of wavelengths to which the eye is sensitive ranges from about 400 to 700 milli microns.
Objects in the visual environment often emit or reflect light waves in a limited area of this visual spectrum, absorbing light waves in other areas of the spectrum.
The dominant wavelength being “seen” is the one that we come to associate with a specific color name. The visible color spectrum and the names commonly associated with the various light wavelengths
A color posses three properties
· Hue is the spectral wavelength composition of a color. It is to this we attach a meaning such as green or red.
· Chroma or saturation is the purity of a color in a scale from gray to the most vivid version of the color. The more saturated a hue is, the more visible it is at a distance.
· saturated, the less visible it is. Value or intensity is the relative lightness or darkness of a color in a range from black to white.
The long-wavelength colors (red) are commonly referred to as warm, and shortwavelength colors (blue) as cool.
Color, then, is a combination of hue, chroma, and value.(HSV) or primary wavelength colors RGB
The eye is never steady, instead trembling slightly as we see.
If pixels of different colors are placed next to each other, this tremor combines the two colors into a third color. This is referred to as dithering, and sometimes texture mapping.
Taking advantage of this phenomena, an optical illusion, a third color can be created on a screen. Dithering is often used to create a gray scale when only black and white pixels are available to work with.
Use color to assist in formatting a screen:
Relating or tying elements into groupings.
Breaking apart separate groupings of information.
Associating information that is widely separated on the screen.
Highlighting or calling attention to important information by setting it off from the other information.
Use color as a visual code to identify:
The logical structure of ideas, processes, or sequences.
Sources of information.
Status of information.
Use color to:
Realistically portray natural objects.
Increase screen appeal.
Possible Problems with Color
When used improperly, color may even impair performance by distracting the viewer and interfering with the handling of information.
Possible problems may be caused by the perceptual system itself or the physiological characteristics of the human eye.
High Attention-Getting Capacity
This quality causes the screen viewer to associate, or tie together, screen elements of the same color, whether or not such an association should be
The result is often bewilderment, confusion, and slower reading.
Interference with Use of Other Screens
Indiscriminate or poor use of color on some screens will diminish the effectiveness of color on other screens.
Varying Sensitivity of the Eye to Different Colors
All colors are not equal in the eye of the viewer. The eye is more sensitive to those in the middle of the visual spectrum (yellow and green), which appear brighter than those at the extremes (blue and red). Thus, text composed of colors at the extremes is thought to be more difficult to read.
The wavelengths of light that produce blue are normally focused in front of the eye’s retina, the red wavelengths behind it.
Simultaneous or sequential viewing of red and blue causes the eye to continually refocus to bring the image directly onto the retina, thereby increasing the potential for eye fatigue.
The perceived appearance of a color is also affected by a variety of other factors, including the size of the area of color, the ambient illumination level, and other colors in the viewing area.
Also, larger changes in wavelength are needed in some areas of the visual spectrum for a color change to be noticed by the eye. Small changes in extreme reds and purples are more difficult to detect than small changes in yellow and blue-green.
A red viewing deficiency is called protanopia, a green deficiency is called deuteranopia, and a blue deficiency is called tritanopia.
These common color deficiencies, their results, and the percentage of people who experience these problems are given below
Cross-Disciplinary and Cross-Cultural Differences
Colors can have different meanings in different situations to different people.
The same color may also have a different connotation, depending upon its viewer. The color blue has the following quite different meanings:
· For financial managers—Corporate qualities or reliability. o For health care professionals—Death.
· For nuclear reactor monitors—Coolness or water.
· For American movie audiences—Tenderness or pornography.
Color appeal is also subjective. People have different tastes in color, what is pleasing to one person may be distasteful or unusable by someone else
Color and Human Vision
To understand how color should be used on a screen, it is helpful to know something of the physiology of the human eye.
Muscles control the lens of the eye. These muscles focus received wavelengths of light on the retina.
The lens itself is not color corrected. The wavelengths of light that create different colors are focused at different distances behind the lens, the longer wavelengths (red) being focused farther back than the shorter wavelengths (blue).
The result is that colors of a different wavelength from the color actually being focused by the lens will appear out of focus. To create a sharp image of the out-of-focus colors requires a refocusing of the eye.
Very pure or saturated colors require more refocusing than less pure or unsaturated colors. Therefore, a color with a large white component will require less refocusing.
The lens does not transmit all light wavelengths equally. It absorbs more wavelengths in the blue region of the spectrum than those in the other regions.
The retina is the light-sensitive surface of the eye.
It comprises two kinds of receptors, rods and cones, which translate the incoming light into nervous impulses.
Rods are sensitive to lower light levels and function primarily at night.
Cones are stimulated by higher light levels and react to color. The sensitivity of cones to colors varies, different cones possessing maximum sensitivity to different wavelengths of light.
Rods and cones vary in distribution across the retina. The center is tightly packed with cones and has no rods. Toward the periphery of the retina, rods increase and cones decrease.
Thus, color sensitivity does not exist at the retina’s outer edges, although yellows and blues can be detected further into the periphery than reds and greens.
The brightness sensitivity of the eye to different colors also varies. It is governed by output from the red and green cones.
The greater the output, the higher the brightness, which results in the eye being most sensitive to colors in the middle of the visual spectrum and less sensitive to colors at the extremes.
The components of the eye—the lens and retina—govern the choices, and combinations, of colors to be displayed on a screen. The proper colors will enhance performance; improper colors will have the opposite effect,
When choosing colors for display, one must consider these factors:
· the human visual system,
· the possible problems that the colors’ use may cause,
· the viewing environment in which the display is used,
· the task of the user, how the colors will be used, and
· the hardware on which the colors will be displayed
Choosing Colors for Categories of Information
Choosing colors for categories of information requires a clear understanding of how the information will be used.
· If different parts of the screen are attended to separately, color-code the different parts to focus selective attention on each in turn.
· If decisions are made based on the status of certain types of information on the screen, color-code the types of status that the information may possess.
· If screen searching is performed to locate information of a particular kind or quality, color-code these kinds or qualities for contrast.
· If the sequence of information use is constrained or ordered, use color to identify the sequence.
· If the information displayed on a screen is packed or crowded, use color to provide visual groupings.
Use color as a redundant screen code.
Colors in Context
Colors are subject to contextual effects. The size of a colored image, the color of images adjacent to it, and the ambient illumination all exert an influence on what is actually perceived.
At the normal viewing distance for a screen, maximal color sensitivity is not reached until the size of a colored area exceeds about a 3-inch square.
Adjacent images can influence the perceived color. A color on a dark background will look lighter and brighter than the same color on a light background
Colors also change as light levels change. Higher levels of ambient light tend to desaturate colors. Saturated colors will also appear larger than desaturated colors.
Design for monochrome first.
· in shades of black, white and gray.
· Doing this will permit the screen to be effectively used:
o By people with a color-viewing deficiency.
o On monochrome displays.
o In conditions where ambient lighting distorts the perceived color.
o If the color ever fails.
Use colors conservatively.
Do not use color where other identification techniques, such as location, are available.
Discrimination and Harmony
For best absolute discrimination, select no more than four or five colors widely spaced on the color spectrum.
Good colors: red, yellow, green, blue, and brown.
For best comparative discrimination, select no more than six or seven colors widely spaced on the color spectrum.
Other acceptable colors: orange, yellow-green, cyan, violet, and magenta.
Choose harmonious colors.
One color plus two colors on either side of its complement.
Three colors at equidistant points around the color circle.
For extended viewing or older viewers, use brighter colors.
To draw attention or to emphasize elements, use bright or highlighted colors. To deemphasize elements, use less bright colors.
The perceived brightness of colors from most to least is white, yellow, green, blue, red.
To emphasize separation, use contrasting colors.
Red and green, blue and yellow.
To convey similarity, use similar colors.
Orange and yellow, blue and violet.
To indicate that actions are necessary, use warm colors.
Red, orange, yellow.
To provide status or background information, use cool colors.
Green, blue, violet, purple.
Conform to human expectations.
· In the job.
· In the world at large.
Some common color associations are the following:
· Red—Stop, fire, hot, danger.
· Yellow—Caution, slow, test.
· Green—Go, OK, clear, vegetation, safety.
· Blue—Cold, water, calm, sky, neutrality.
· Warm colors—Action, response required, spatial closeness.
· Cool colors—Status, background information, spatial remoteness.
Some typical implications of color with dramatic portrayal are:
· High illumination—Hot, active, comic situations.
· Low illumination—Emotional, tense, tragic, melodramatic, romantic situations.
· High saturation—Emotional, tense, hot, melodramatic, comic situations. o Warm colors—Active, leisure, recreation, comic situations.
· Cool colors—Efficiency, work, tragic and romantic situations.
In the center of the visual field, use red and green.
For peripheral viewing, use blue, yellow, black, and white.
Use adjacent colors that differ by hue and value or lightness.
Order colors by their spectral position.
Red, orange, yellow, green, blue, indigo, violet.
Foregrounds and Backgrounds
· Use colors that highly contrast with the background color.
· For text or data, use:
o Desaturated or spectrum center colors such as white, yellow, or green.
o Warmer more active colors.
· Use colors that possess the same saturation and lightness.
· To emphasize an element, highlight it in a light value of the foreground color, pure white, or yellow.
· To deemphasize an element, lowlight it in a dark value of the foreground color.
· Use a background color to organize a group of elements into a unified whole.
· Use colors that do not compete with the foreground.
· Light-colored backgrounds of low intensity: Off-white or light gray.
· Desaturated colors.
· Cool, dark colors such as blue or black.
· Colors on the spectral extremes.
Use at least five colors or color values to create a 3-D look on a screen.
Background: The control itself and the window on which it appears.
Foreground: Captions and lines for buttons, icons, and other objects.
Usually black or white.
Selected mode: The color used when the item is selected.
Top shadow: The bezel on the top and left of the control.
Bottom shadow: The bezel on the bottom and right of the control.
Motif has created an algorithm to automatically calculate the top and bottom shadows, and the select color based upon the background (Kobara, 1991). Briefly, it recommends the following:
Background. Midrange colors, 155–175 on the RGB scale.
Foreground. Black or white, depending on the lightness or darkness of the background.
Selected mode. About 15 percent darker than the background color, halfway between the background and bottom shadow. (Calculate this by multiplying the background color’s RGB value by 0.85.)
Top shadow. About 40 to 50 percent brighter than the background color.
(Calculate this by multiplying the background color’s RGB by 1.50.)
Bottom shadow. About 45 to 60 percent darker than the background color. (Calculate this by multiplying the background’s RGB values by 0.50.)
Color Palette, Defaults, and Customization
Permit users to customize their colors.
Provide a default set of colors for all screen components.
Provide a palette of six or seven foreground colors.
Provide 2 to 5 values or lightness shades for each foreground color.
Provide a palette of six or seven background colors.
Never refer to a screen element by its color.
For fine discriminations use a black-gray-white scale.
· Recommended values are white, light gray, medium gray, dark gray, black.
Text in Color
When switching text from black to color:
· Double the width of lines.
· Use bold or larger type:
· If originally 8 to 12 points, increase by 1 to 2 points.
· If originally 14 to 24 points, increase by 2 to 4 points.
Check legibility by squinting at text.
· Too-light type will recede or even disappear.
At the standard viewing distance, white, orange, or green are acceptable colors.
At a far viewing distance, white is the best choice.
Over all viewing distances, from near to far, white is the best choice.
Cultural, Disciplinary, and Accessibility Considerations
Consider the impact of specific colors on:
· Users of various cultures.
· Users of various disciplines.
· Users with color-viewing deficiencies.
· Users relying on accessibility utilities.
Choosing Colors for Textual Graphic Screens
For displaying data, text, and symbols on a textual graphical screen colors selected should have adequate visibility, meaning, contrast, and harmony.
Use effective foreground/background combinations.
Use effective foreground combinations.
Choose the background color first.
Display no more than four colors at one time.
Use colors in toolbars sparingly.
Test the chosen colors.
Effective Foreground/Background Combinations
Lalomia and Happ (1987) established effective foreground/background color combinations
From a color set of 16 different foregrounds and 8 different backgrounds, 120 color combinations were evaluated for (1) response time to identify characters, and (2) subjective preferences of users.
The results from each measure were ranked and combined to derive an overall measure of color combination effectiveness.
The best and poorest color combinations are summarized in Table given below
The results yield some interesting conclusions:
· The majority of good combinations possess a bright or high-intensity color as the foreground color.
· The majority of poor combinations are those with low contrast.
· The best overall color is black.
· The poorest overall color is brown.
· Maximum flexibility and variety in choosing a foreground color exists with black or blue backgrounds.
· Brown and green are the poorest background choices.
Bailey and Bailey (1989), in their screen creation utility Protoscreens, have a table summarizing research-derived good foreground/background combinations.
Uses of Color to Avoid
Relying exclusively on color.
Too many colors at one time.
Highly saturated, spectrally extreme colors together:
Red and blue, yellow and purple.
Low-brightness colors for extended viewing or older viewers.
Colors of equal brightness.
Colors lacking contrast:
For example, yellow and white; black and brown; reds, blues, and browns against a light background.
Fully saturated colors for text or other frequently read screen components.
Pure blue for text, thin lines, and small shapes.
Colors in small areas.
Color for fine details.
Red and green in the periphery of large-scale displays.
Adjacent colors that only differ in the amount of blue they possess.
Single-color distinctions for color-deficient users.
Using colors in unexpected ways.
Using color to improve legibility of densely packed text.