General Information on Color Deficits

Color vision deficiency (commonly referred to as "color blindness") is a condition in which certain colors cannot be distinguished or can only be distinguished with difficulty. It is most commonly due to an inherited condition. There is no treatment.

Red/Green color blindness is by far the most common form. Blue/Yellow and other forms also exist, but are more rare and harder to test for. Complete color blindness (seeing only in shades of gray) is extremely rare. Color deficiencies of one sort or another occur in about 8% - 12% of males and about 1/2 - 1% of females (of European origin).

Clinically, disturbances of color vision will occur if the amount of pigment within a cone is reduced or if one or more of the three cone systems are entirely absent. The gene for this is carried in the X chromosome. therefore color blindness occurs much more commonly in males and is typically passed to them by their mothers. Reduction in pigment in one or more channels is more common than the loss of one or more sets of cones; therefore, most have a strict color deficiency, and perceive certain color channels more poorly, vs. not at all.

Types of color deficiency

Protanomaly (partial red-green, 1% of males) - Also known as "red-weak." Complete or partial inability to see using long-wavelength sensitive retinal cones making hard to distinguish between colors in the green-yellow-red section of the spectrum. Reds perception is reduced both in saturation and brightness. Red, orange, yellow, yellow-green, and green appear somewhat shifted in hue towards the green, and all appear paler than they do to the normal observer. The redness component that a normal observer sees in a violet or lavender color is so weakened for the protanomalous observer that he may fail to detect it, and therefore sees only the blue component.

Deuteranomaly (partial red-green, 5% of males, the most common form of color blindness) - Also known as "green weak." Complete or partial inability to see using middle-wavelength sensitive retinal cones making hard to distinguish between colors in the green-yellow-red section of the spectrum. He makes errors in the naming of hues in this region because they appear somewhat shifted towards red for him - difficulty in distinguishing violet from blue.

Dicromasy

Individuals with the following two conditions normally know they have a color vision problem and it can effect their lives on a daily basis. They see no perceptible difference between red, orange, yellow, and green. All these colors that seem so different to the normal viewer appear to be the same color for this two percent of the population.

Deuteranopia (complete red-green, 1% of males) - The deuteranope suffers the same hue discrimination problems as the protanope, but without the abnormal dimming. The names red, orange, yellow, and green really mean very little to him aside from being different names that every one else around him seems to be able to agree on. Similarly, violet, lavender, purple, and blue, seem to be too many names to use logically for hues that all look alike to him.

Protanopia (complete red-green, 1% of males) - For the protanope, the brightness of red, orange, and yellow is much reduced compared to normal. This dimming can be so pronounced that reds may be confused with black or dark gray, and red traffic lights may not appear to be illuminated at all. They may learn to distinguish reds from yellows and from greens primarily on the basis of their apparent brightness or lightness, not on any perceptible hue difference. Violet, lavender, and purple are indistinguishable from various shades of blue because their reddish components are so dimmed as to be invisible e.g. Pink flowers, reflecting both red light and blue light, may appear just blue to the protanope.

Less-Common Color Deficit Conditions

Tritanopia (complete blue-yellow)

Tritanomaly (partial blue-yellow) - Complete or partial inability to see using short-wavelength sensitive retinal cones making hard to distinguish between colors in the blue-yellow section of the spectrum.

Monochromacy - Complete or partial inability to distinguish colors. Complete color blindness is very rare.

Common Usability Complaints for Colorblind Individuals

• Weather forecasts and similar info-graphical maps. Certain colors cannot be distinguished in the map or legend.
• Lighted indicators (e.g. charging LED). Is the indicator light red, yellow, or green?
• Position is often the only way to decipher traffic lights -- this is an important reason they are standardized with red on top. Horizontal signals, or single signals that change color, are a problem.
• Color observation by others: "Look at those lovely pink flowers on that shrub". My reply, looking at a greenish shrub "What flowers?"
• Kids and crayons: Color vision deficiencies bother affected children from the earliest years. At school, coloring can become a difficulty when one has to take the blue crayon -and not the pink one- to color the ocean.
• Chemical test strips (e.g. for hard water, pH, swimming pools).
• When cooking, red deficient individuals cannot tell whether their piece of meat is raw or well done. Many can not tell the difference between green and ripe tomatoes or between ketchup and chocolate syrup. They can however distinguish some citrus fruits. Oranges seem to be of a brighter yellow than that of lemons.

Design Patterns for Users with Color Deficits

Design patterns to design around users with a color deficit (e.g. colorblindness) are available at WeAreColorblind.com. These are heavily focused on infographics, but the principles are easy to follow.

Color Deficit Simulators

• Sim Daltonism - Color blindness simulator for OSX, shows results much like the Apple Digital Color Meter.

• Vischeck - Color simulator plugins for Photoshop.

• Entre - Web-based color blindness simulator. Upload any graphic to test.

• Wickline - Web-based color blindness simulator. Specify a URL to see the resulting page modified.

Other Color Deficit Design Tools & Resources

• Colorlab - lets you pick from a (websafe) palette, and see the results. Seems to have a lot more information, all to help you understand how to pick colors safe for color-deficit users, but I am not totally up on how it works yet.

• Ishihara Test for Color Blindness