If you or someone you know isn’t color blind, you might not ever think of it. However color blindness is a serious consideration which must be accounted for when designing publicly available work since around 7-10% of males are color blind, generally to red-green. Color blindness is also higher in Caucasian men than other races and rarely ever affects women.
Background on the Human Eye
The human eye has rods and cones. In simplest terms, the cones see color and the rods are much more sensitive to variations in amount of light. Your night vision comes from the rods which detect very subtle differences in light level, however the rods can take up to 30 minutes to fully adjust to night vision (which is why high beams at night in your face is such a problem). The rods also are virtually unable to detect red light so red taillights, red lights on your dashboard, red flashlights all maintain your night vision.
Variations in Color Blindness
The most common color blindness is red-green. This means that the person (generally man) can not distinguish between red and green. However, like most things in life, color blindness comes in shades. Some men will be able to differentiate a good portion of reds and greens and only have trouble with a few, while others will be completely unable to tell red from green. For these people walking into a fruit and vegetable section looks very very green.
Red-green is by far the most common, however it is possible to find someone who is green-blue blind. For these people they basically see everything as red and blue, which means that a lot of things look pink. Being completely unable to see color is extremely rare, those people really just see things in grayscale.
Simple Trick: Use Grayscale
Since colorblindness affects the perception of color, one of the easiest ways to test your design for how people with various types of colorblindness would see is to use grayscale. If your design still comes across well in grayscale, then people who are color blind should be able to appreciate it.
More Advanced: Color Tools
Another option if checking for particular color blindness is going to come up regularly is to use some of the available software tools. A very easy to use and freely available tool that I like is Color Oracle. This tool is a small download and quick install which adds an item to your menu bar. Just click it and select which type of color blindness you would like to check for. One of the advantages of this tool is that it works across your entire computer — no matter what application is open.
Another option for designers are tools such as the integrated color blindness proofing abilities in Photoshop CS4 and above. With these you can easily view your color blind versions of a file alongside the full color. One of the advantages here for designers is being able to show others how a given design will look to various people who are color blind.
Morale of the Story
If you are doing a design which will likely be viewed by men (especially if it will be primarily viewed by men), you need to take into consideration your choices of color, especially when they come to red and green. Strong bright colors tend to work very well whereas subtle changes of hue can definitely cause problems. And generally when using a green, do what a number of modern traffic lights do: mix a little blue into the green, it’s subtle but it works.