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Why does Jenkins have blue balls?

R. Tyler Croy
R. Tyler Croy
March 13, 2012

A japanese traffic light It is interesting having an open source project that is sufficiently old to start generating "lore" of some form or another. Jenkins is starting to get to be that age, having been started over 6 years ago.

One of the most commonly asked questions, is about Jenkins' use of "blue balls" to indicate success by default. This is enough of an "issue" for some users that the Green Balls plugin is in the list of top 10 installed plugins.

The reason behind our use of blue to indicate success has its basis in Kohsuke’s Japanese upbringing. The cultural differences were enumerated in a bug report comically titled "s/blue/green/g" (JENKINS-369):

This response Kohsuke cited was taken from this Q&A thread

Q. "Why do Japanese people say that they have blue traffic lights when they are really green?" --Question submitted by John Sypal

A: According to the book, Japan From A to Z: Mysteries of Everyday Life Explained by James and Michiko Vardaman, the first traffic signals in Japan were blue instead of green, but the blue lights were difficult to see from a long distance away so they were replaced with green ones. Vardaman says that the custom of referring to traffic lights is a holdover from those days.

This sounds like a good explanation, but the problem with it is that you will hear Japanese people refer to other green things (like cucumbers, spinach, and sometimes grass) as being blue as well. This is because historically, Japanese people considered green to be a shade of blue. For example, the Chinese character for blue, pronounced ao is made up of two characters, iki (life) and i (well) and refers to the colour of plants which grow around a well, a colour between green and blue. When Chinese people see the character, they say it means green, but Japanese people say it means blue.

Japanese books on colours tell us that there are four tertiary colours: red, blue, white and black, and that all others are shades of those four main ones. Ao, therefore, is a sort of ideal blue, halfway between green and blue. The sky is said to be blue, but it is a different shade of ao than a traffic light is. Tree leaves are said to be green, but green is a shade of ao, like crimson is a shade of red.

In another interesting cultural difference relating to colour, Japanese children always colour the sun red instead of yellow.

Unfortunately it’s not for color blind users, although that’s a pretty convincing explanation. Jenkins has blue balls because in Japan, red means stop and blue means go!

Image courtesy of this site

About the author

R. Tyler Croy

R. Tyler Croy

R. Tyler Croy has been part of the Jenkins project for the past seven years. While avoiding contributing any Java code, Tyler is involved in many of the other aspects of the project which keep it running, such as this website, infrastructure, governance, etc.