Have you ever wondered why a blue sphere signifies a successful Jenkins build job, rather than the more traditional green? A developer can install the Jenkins Green Balls plugin to rectify this issue and conform to the standard red, yellow and green pattern for breakage, failure and success.
However, the question still remains: Why does blue represent a successful Jenkins build job instead of green? In a recent interview with Jenkins creator Kohsuke Kawaguchi, TheServerSide asked that very question. Apparently, the answer stems from an interesting cultural nuance in Kawaguchi's native Japan.
Blue spheres vs. green balls
"In Japan, green and blue are not all that distinguished," Kawaguchi said. "We often use the single word blue to cover quite a range of green as well." Kawaguchi said that, in Japan, a traffic light is said to have a blue light. "It's not that the actual color of the lights are different when you go there."
So, when Kawaguchi originally chose images for the Jenkins UI, he naturally looked for a blue icon, not green. "When I wrote the first Jenkins program that had the icon, for me, it was very natural to draw it using blue."
Jenkins Green Balls plugin
Of course, Jenkins users aren't permanently bound by the blue sphere. Jenkins' plugin-based architecture makes it incredibly easy to customize the tool. For example, there is a Green Balls plugin that can be accessed from its update site that will show a successful Jenkins build job as a green sphere instead of a blue one.
One thing to keep in mind with the Jenkins Green Balls plugin is whether or not any users are colorblind and can't distinguish between green and yellow. Blue could be a more discernible option for these users if they are colorblind.
If you choose not to install the Green Balls plugin, you can pass along this unique factoid to new users whenever they bring up this question about why successful Jenkins build jobs look the way do.