Contrast and color
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Color considerations
Two color patches may be perceived as being exactly the same color, yet the
distribution of wavelengths may be very different. The eye cannot analyze
the color, that is, it cannot determine the actual combination of wavelengths
that produces the perception of a particular hue or color.
Reproducing colors by mixing a combination of primary colors, or known color
components, is common in the paint and dye industries as well as in color
printing, color photography and color television. The process used in color
printing may be observed with a magnifying glass. The picture is seen as a
series of dots of primary colors. Without magnification, the eye blends the
individual colors together to produce the intended color picture.
Color Television works in a similar way, except that the screen generates
the colors rather than subtracts them from white as in the case of color printing.
The typical color television set is like three monochromatic sets, each one
producing images of green, red or blue. When the three images are superimposed,
they are integrated by the eye and continuous hues are perceived.
Blue light is refracted more than red light and may be used advantageously
for special displays that are to be used at closer than normal viewing distances.
The opposite may be true, however, for displays that are to be viewed at distances
of more than two or three meters. The eye is slightly myopic to blue light,
and distant blue light may not be brought into proper focus. In addition,
blue should not be used for tasks that require the perception of fine detail.
Blue receptors are found in reduced numbers or are absent in the central part
of the fovea. That reduces the acuity for blue targets in that region of the
retina.
Color Vision Anomalies
There certainly are situations where the use of color and color coding is advantageous.
It should be kept in mind, however, that defective color vision may be inherited
or acquired by disease or accident. The results of acquired defective color
vision are difficult to predict. They are most often associated with poor
discrimination, however, in the blue-green region and a loss of acuity.
Most people with color deficiencies should be able to use a common three-primary
multicolor display that would present fixed combinations of the primaries
to produce white and six colors. A person with no color vision, an achromat,
would see all those colors as some level of white. Achromats make up about
0.005% of the population. Persons with some form of color deficiency, such
as deuteranopes and protanopes, may see each of those seven colors as being
different. For these people, the difference between red and green may be similar
to the difference a person with normal color vision might see between two
distinct shades of the same color. People with color deficiencies tend to
make errors, and in order to minimize such errors, they take longer to perform
the task (Bergman and Duijnhouwer, 1980).
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