Don't Indicate Status with Just Color

Note: Since this article was written, AxoCover added configuration of colors in the settings dialog. The original point, though, was that you shouldn't indicate status with just color in your own projects.

There is a flaw in the AxoCover code coverage tool: The colors used for coverage, red and green, are hard coded. If someone were red/green color blind, this tool would be difficult to use. That creates difficulty for 8% of men and 0.5% of women. Showing status with hard coded colors with no other visual indicator is a mistake in user interface design, not just in AxoCover but in all programs. Either colors must be configurable, or an additional way of differentiating the colors (such as hatching one of them) should be used.

Status indicated with red and green bars

You'll notice that a traffic stop light indicates color with both red and green, but also with position of the colors; it does not have one light that changes color.

Traffic light uses both color and position to indicate status

Indicating status with just color, particularly red and green, is a very common UI mistake among programmers who are not color blind. While I am not color blind, I try to be aware of places where color is used wrong. This is not just an inconvenience to some people. In some cases, particularly in the United States which has the Americans with Disabilities Act (ADA), using just color to indicate status might be a violation of the law, and could have legal repercussions.