1. Green Apples, Seaweed, and Juice Are Called "Blue" in Japan
In a vegetable shop, green apples are labeled as "blue apples." Caterpillars, seaweed, and green juice are also called "blue," even though they look green to us. Older words like "blue leaves" or "blue goods" (meaning vegetables) also use this pattern.[3]
This is not just a lingering error in speech. The difference comes from how the word ao was used long ago versus how we use it now. Today, when people hear "blue," they think of a specific color. In the past, ao covered a much broader range. So, how wide was that old definition?[3]
2. The Old Japanese Word "Ao" Covered Colors from Blue to Green
Dictionaries explain that ao used to be a general term for colors ranging from deep indigo (blue-black) to yellowish-green.[2]
In ancient Japanese, what we now call green was also described as ao. One theory suggests that early Japanese only had four basic color names: red, black, white, and blue. If there are fewer color names, each word must cover a wider range of colors. This fits with the idea that green was included in "blue."[1]
The range of ao was not limited to just green. In horse racing, a term for coat color is "blue hair" (aoge). This actually refers to black horses. The Japan Racing Association explains that the tips of their fur can turn brownish depending on the season, making them look like dark bay or blue-bay.[6]
So, how did "green" separate from this broad "blue"?[2]
3. The Word "Midori" Originally Meant Fresh Plant Sprouts
The word midori originally referred to fresh new sprouts of plants.[3]
The core meaning was about freshness and vitality, rather than the hue itself. Traces of this remain in modern expressions. A newborn baby is called midorigo (green child), and shiny black hair is praised as "green hair." They describe freshness, youth, or luster.[1]
The use of midori as a color name can be traced back to the *Man'yoshu*, a poetry anthology from the Nara period. A poem there says, "In spring it sprouts; in summer it is green." However, some sources suggest the term appeared as early as the Heian period. It is safest to think of this transition happening between the Nara and Heian periods.[3]
Even after midori became a color name, dictionaries note that blue and green were not always clearly distinguished in usage. When did they finally split?[3]
4. How Blue and Green Became Separate Color Names After the Heian Period
Researchers suggest that blue and green became distinct color names between the end of the Heian period and the Kamakura period.[4]
One clue is the poetic phrase aoni yoshi, often used to introduce Nara. In one theory, ao refers to the fresh green of trees, and ni (red) refers to the red pillars of temples, creating a contrast between green and red.[5]
However, another explanation says that aoni was an old name for a green pigment. If this is true, we cannot determine the color of ao from this phrase alone. The origin of these words has multiple theories, and no single answer is certain.[5]
If blue and green separated so long ago, why are traffic lights still called "blue"?[4]
5. Why Japan's Green Traffic Lights Are Called "Blue"
The first automatic traffic signal in Japan was installed at the Hibiya intersection in Tokyo in 1930. It was imported from the United States. Newspapers at the time reported the light colors as "red, yellow, and blue."[7]
Some official documents from 1933 used the term "green signal," but by 1947, laws changed the name to "blue."[8]
Dictionaries explain that the traffic light remains called "blue" because it is a remnant from a time when blue and green were not distinguished. It is in the same category as green apples or caterpillars being called blue.[2]
Why, then, are so many green things linked to "blue"?[7]
6. Why "Blue" (Ao) Is Linked to Youth and Immaturity
In the old Five Elements theory, ao was associated with wood. This linked it to youth and immaturity.[2]
Wood sprouts and grows in spring. This idea may connect to using "blue" for things that are not yet ripe, like green apples. However, dictionaries only state that ao symbolized youth and immaturity; they do not directly link this theory to the specific phrase "green apple."[2]
The word midori also described the freshness of new sprouts. Both ao and midori can be understood as words for things that are young, lively, and full of life.[2]
7. Activity: Find "Blue" Words for Green Things in Your Home
Look at food labels in your kitchen or words in books and encyclopedias. You will find items like seaweed, shiso, green onions, and green juice labeled with the word for blue.[3]
When you find them, look at the actual color and write down whether it is green or blue. Finally, count how many are actually green. This will show you how many words starting with "blue" refer to green things.[3]
You can also look up "blue" and "green" in a Japanese dictionary at home to compare the explanations you read here. Libraries may have books on the history of color names in Japanese.[1]