The light in front of you changes from yellow, to red. Naturally you interpret yellow to mean “slow down,” and red to mean “stop.” So you patiently wait for the signal to turn green – unless of course you are in Japan, and then you wait for it to turn blue. While a stubborn few might insist that the lights in Japan are different from the rest of the world and are, or once were truly a shade of blue, this line of reasoning does not survive closer scrutiny. For people who have a working knowledge of Japanese, it becomes apparent that mislabeling green things as blue is very common in the language. Unripe fruit is described as being blue. In fact all green vegetables, ripe or otherwise are often referred to as *aomono* or “blue-things.” Caterpillars are called “blue bugs.” Much in the same way an inexperienced or immature person might be called “green” in English, Japanese would call these people *aokusai* – “blue smelling.” This goes on and on through the language, with blue apples, blue snakes, and so on. Even those few who refuse to budge on the traffic signal issue can agree that apples, caterpillars and vegetables are green.

There is no consensus on how or why this mislabeling occurs throughout the Japanese language, but one of the most common theories is that long ago, the Japanese language had no specific word for the color green. Green was a type of blue. Run the words 碧 or 蒼 through your favorite translation software to see that various forms of the word blue are in fact translated as both green and blue. Ancient Japanese did not differentiate between the two, nor in fact, traditionally were there names for orange or purple. Everything from green to purple was considered blue, and everything from orange to crimson was considered red. For people comfortable with basic Japanese, there is a simple test to see if a color is an original Japanese word, or if it was added later – a sort of etymological legacy. If you can change the noun form into an adjective by simply adding the sound “i” to the end, as in *aoi, akai, shiroi, kuroi* then you have just discovered the original color families. If instead, you have to add the word *iro* to the end, as in *chairo, daidai-iro, *or *momo-iro*, then it was added much later. You might also notice that such colors are typically named after something in nature, such as *peach color *for pink*, water color *for light blue*, mouse color* for grey and so on. Contrarily blue, red, black and white have no meaning outside of the color itself.

If this theory is to be believed, then it still leaves the question of where the modern word *midori* came from. Most likely it comes from an archaic Japanese word *midoru* which means “to come into leaf.” This is similar to the word “in bloom” for flowers, referring to leaf sprouts instead. Over time the original use of the word dropped out of use, but the color of the buds or sprouts remained as the current color *midori-iro*.

But linguistics aside, there is a more deep-seated, biological reason why the traffic lights are in fact green. It has been suggested that not only humans, but all mammals see the color red as a warning sign, and green as a sign of safety. This most likely stems from the fact that mammal blood becomes red when oxidized, and instinctively causes us to feel alert. Examples of this can be readily found in nature with poisonous berries, even poisonous insects adopting red patterns to warn would-be predators. Green on the other hand means edible plants and shelter. This is especially true for arboreal species such as primates – namely humans, who seek refuge in green areas when in danger. For this reason, relying on animal instinct, green is the natural color to mean “go” and red is the obvious choice for “stop” or “danger.” It makes one wonder however, if things are opposite for insects, whose cuprous blood turns green when oxidized, instead of turning red like our ferrous blood. Would mosquito traffic lights be opposite from ours, where green means blood, and red means food?