Approximately 5% to 8% of men and 0.5% of women are born colorblind. Usually, these people are categorized as protans (red weak) and/or deutans (green weak). Though there are varying degrees of color blindness, there are some that cannot differentiate red from green, so the colors look the same to them.
When you are designing an HMI or a SCADA display, you have to consider color blindness.
This is a big problem in industry, where red and green are commonly used to indicate the status of a piece of equipment.
There are a couple of ways to solve this problem. We could use icons that have different shapes, depending on whether they are on or off. In addition to being a different color, a pump icon that is off could have a round hole cut out in the middle, such as is shown below.
Here is an approximation of what the pumps shown above might look like to a person who is colorblind.
The black dot in the middle of the pump that is off will be appreciated.
Another option is to add text. Not only does this help the person who might be colorblind, it obviously confirms the state of the equipment to those even with true color vision.
An interesting benefit to keeping the icons discernible to the color blind is that these icons are easier to read for those of us who are not color blind.
Excerpted from How to Program RSView32