• Color Deficit Design Tools

Mobile devices are used in all sorts of environments, and must be clear and easy to read when bright, dark, dirty, rain-covered, and so on. General heuristic principles should be followed to dual- (or triple-) encode information so that it is clear in all conditions.

Therefore, the design of mobile devices should not be significantly affected by consid- erations for users with color vision deficits. Practically, many, many interfaces are still single-coded, with (for example) red type used for important notices and no use of iconography or type weight to reinforce this.

The information and guidelines in this appendix should serve not just as a reminder of how to address the needs of a significant portion of the population, but also of how color vision can fail every user in certain conditions. If colorblind users are considered in de- sign, the product will work better for all users.

General Information on Color Deficits

Color vision deficiency (commonly referred to as colorblindness) 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 colorblindness is by far the most common form. Blue/yellow and other forms also exist, but are rarer and harder to test for. Complete colorblindness (seeing only in shades of gray) is extremely rare. Color deficiencies of one sort or another occur in about 8% to 12% of males and about 0.5% to 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, colorblindness 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, versus not at all.

Types of color deficiency

The following are various 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 it hard to distinguish between colors in the green- yellow-red section of the spectrum. Red perception is reduced both in saturation and in brightness. Red, orange, yellow, yellow-green, and green appear somewhat shifted in hue toward 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 it 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 toward 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 affect 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 2% 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. He 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