The limitations of color-blind vision
I’m color blind. When I divulge that information to people with normal color vision, they usually respond, “Really? Can you see any color? What color is this?”, as they point to something within close range.
This seemingly innocuous reaction indicates a general lack of understanding and empathy for people who live with this genetic-based vision disability. Color blind people experience many barriers and frustrations when using items that are designed for people with normal color vision.
In this two-part series:
Part 1 provides information about color blindness and its limitations.
Part 2 provides tips to reduce design oversights that affect people with color blindness.
Most of the people with color blindness (about 8% of males and 0.5% of females) can see color in a reduced color spectrum compared to people with normal color vision. Color vision deficient is a more accurate term than color blindness. Only in rare cases does color blindness mean seeing the world in black and white, or through a range of gray tones.
From a physiological perspective, our eyes contain photoreceptor cells that are named rods and cones, based on their shape. Rods number about 120 million per eye, and sense light and dark. Cones number six to seven million per eye, are less sensitive to light, and sense more color. Each of three cone types senses one of three primary colors: blue, green, or red. The information that these three cone types receive, when combined, is what our eyes perceive as color.
In people with a color vision deficiency, one or more cone types is malfunctioning or missing. As a result, they cannot distinguish as many color hues as someone with normal color vision.
The relative lighting (bright, dim, daylight, incandescent, fluorescent), background (light, dark, front lit, and backlit) and size of the color sample all play a role. A color blind person can generally see all primary color hues (red, green, and blue) at full strength (saturation). But the mixture of the deficient hues with other colors makes some colors challenging to identify, or indistinguishable from another.
Contrast is a huge factor in accurately differentiating between color shades. Color gradients (color ramps) are tricky too. One end of the ramp can begin in a hue that is perceptible, and end in a hue that is not. If text appears on top of the color ramp, it is sometimes not readable if the contrast between the elements is not high enough.
The two rows of colors in the following image provide examples of solid colors that can challenge some people with red-green color blindness.
It is relatively easy to differentiate (not identify) the five colors in either horizontal row, as there is good contrast and variation between the color hues.
To the red-green color blind, the colors in the vertical columns are almost identical, depending on the context in which they appear.
As the palette for a pie chart, these ten colors are problematic for most people with red-green color blindness, which is the most common color-vision deficiency.
Anything that involves identification of an item purely by its color can challenge a person with color-blindness. (Examples: matching clothing, plant foliage, signage, LED indicator lights on electrical devices, matching paint colors, colored pencils/crayons, Web sites, user-interface icons, color-coded information charts, board games, sunburn and rashes, insulation colors on electrical wires, maps, GPS color displays).
Color is often used as an element to simplify and differentiate items in the design of a product. Unconsidered color choices make the accessibility of a product more difficult and frustrating for a color blind person. We use color increasingly in the communication of information in many aspects of our society. We can easily reverse accessibility issues by designing products with colors that are perceptible by as many people as possible.
- Colblindor – A Web site dedicated to color blindness, with many articles, and a free eBook.
- We are colorblind – A Web site dedicated to making the Web a better place for the color blind.
- Ishihara Color Blindness Test – The original Ishihara Color Blind test first published in 1917 as an online version.
- Testing Color Vision – Advice for parents and teachers in dealing with color blind children.