Certain color combinations may pose a problem for some people, particularly men. Some studies show that nearly 15% of men have a red/green deficiency. Other research suggests that close to 22% of men have some form of this deficiency.

Women do not suffer from this problem (in any significant numbers), but they should be aware of this fact when selecting colors for visuals, especially because women see the brilliance of all colors.
 
If you happen to have this deficiency, certain “rods and cones” in your eyes may be missing, thus making it difficult for you to pick up the red or green colors of the spectrum. For example, you might see purple more as blue, because you can’t see as much of the red portion of purple. You may see brown more as a green because you can’t see all the red parts that mix with green to make brown.

The deficiency is not as noticeable with large areas of color as it is with small areas. 

For example, suppose a line chart has three lines with one line beige, one line tan, and one line orange. It’s possible that someone with a red/green deficiency will not be able to tell the difference between the three lines. The result will be confusion and a loss of attention.

Try to avoid red-green color combinations, especially in small areas.