Using Color

examples of poor and strong contrast. weak contrast makes things disappear, strong contrast makes things legible.

People with color blindness often have difficulty distinguishing certain colors, such as red and green or blue and yellow. Almost 5% of the population and 8% of men have some form of colorblindness. When color combinations (such as red text on a green background) are of insufficient contrast, the words can actually disappear to a person with colorblindness. You can help prevent this by selecting strong, contrasting color combinations and by labeling things that are otherwise distinguished only by color on a page (think charts and graphs). 

The Gray Scale Test: Print your charts and other graphic in gray scale and give it to someone who knows nothing about the data. Can she read it with ease? Can she distinguish any parts that are not labeled? For example, can she match the colors in the legend to the colors in the chart? For testing text color on background, use this color contrast checker (you are aiming to pass "WCAG AA").

This example is easy to distinguish, but only if you can see the colors as intended:

Original pie chart

Original pie chart example not directly labeled

Same pie chart as seen with two kinds of colorblindness

pie chart as viewed with red blindnesspie chart as viewed with total color blindness

Pie chart using direct labels and texture

pie chart using texture and direct labels