The fact that Greek did not have a word for blue is a myth without any ground.
Already in Homer the word for blue was "cuaneos", which means of the color of "cuanos", like "chruseos" (golden) means of the color of "chrusos" (gold).
"Cuanos" was initially the name for the blue pigment that now is named "ultramarine blue", which was an expensive pigment imported from Afghanistan.
Later, "cuanos" was also used as a name for other cheaper blue pigments that could be used to substitute the expensive ultramarine blue, i.e. for the azurite mined in Cyprus and for the artificial pigment "Egyptian blue".
The English word "cyan" comes from the Greek word "cuaneos", but due to a misunderstanding it is used now for blue-green, despite the fact that it was never used for blue-green by the Greeks. In the Ancient Greece and Rome, when blue-green had to be distinguished from green, it was specified as the color of the beryls, or as the color of turquoise, or as the color of the littoral sea.
While in Greek there was an unambiguous word for blue, what was missing was a word for green. Green is mentioned very rarely in what I have read, and when it is mentioned they use one of the following expressions: the color of the emeralds (smaragdinos), the color of grass (poodes) or the color of leek (praseos).
In the early Greek authors, "chloros" that is now used to mean green in many scientific terms was not used for green, but perhaps for yellow or yellow-green, e.g. Homer uses "chloros" for the color of some honey.
The Romans used the word "viridis" both for green and for blue-green.
Nevertheless, when they wanted to describe more precisely a color, for example when Pliny the Elder had to explain the difference in color between emeralds and beryls, they used expressions like "green like the leaves" or "green like the grass" for green, and "green like the littoral sea" for blue-green.
> The Greek said the sea was green, for example; so did the Romans.
This isn't exactly a surprise; they were both heavily involved with the sea.
English speakers talk about the sea being blue, but that's not because it is blue by the standards of English speakers. It's because most people don't bother to give any thought to the things they say. If you go look at the sea, it is obviously green.
In China, for example, the word for green 綠 is used for the light
綠 is used in Japanese for the color of green tea, but they use 青 for the green light
There's also 翠 in Japanese to mean a bright green, which in Chinese also has a blue connotation (based on the color of the kingfisher who dives 淬 to catch fish)
I'm not doubting that multiple languages have that aspect to it, but as far as I know that does not result in blue traffic lights. I have not heard of an instance of a blue traffic light in China to go with your Chinese example.
This discussion is weird, because the Kanji 青 in Japanese was borrowed from classical Chinese (presumably during the Tang dynasty around the 7th to 9th century).
So using Chinese as an example of "another language" having green-blue confusion isn't very meaningful since modern Chinese aka Mandarin also inherits pretty much the same 青 albeit popular usage differs somewhat.
Yet the fact that there's no blue traffic light in China just hinges on the fact that people don't commonly refer to the "green" in traffic lights as 青 in China (but you could). The word 青 is used to refer to a broad spectrum of green and blue in different contexts, just happens people generally refer to the traffic lights as "綠" instead. And since there's no ambiguity to "綠" there's no confusion of whether the traffic lights should be "green" or "blue", and thus you don't see blue traffic in China (hopefully).
The word "ao" in Old Japanese already had the blue/green confusion before the character 青 was borrowed to write it, so if classical Chinese did as well I guess that would be two such languages.
> The word "ao" in Old Japanese already had the blue/green confusion before the character 青 was borrowed to write it
What would the evidence for this be? It's clear that the word "ao" does not derive from the Chinese pronunciation of 青. But its meaning could easily have shifted under the influence of the spelling. Do we have a source that writes the word without spelling it 青?
The US. They are mostly green, but a lot of them have a blue tint for the colorblind. I suspect other countries as well, colorblindness is very common and this is a simple adaptation.
Yeah and they also don't realise that "one word for two colours" is just nonsensical.
All words are descriptions for a continuous range of colours. Oa apparently just covers a particularly huge range. But you could equally say "ha those stupid English people only have one word for lilac and purple. Idiots!"
You see the same thing in other areas. In Mandarin Chinese, the sounds represented by "si" in English vision or "r" in English virile are the same sound.
An English speaker (like speakers of many other languages) would find this ridiculous, but it is true that the two sounds represent either side of a completely arbitrary threshold applied to a continuous phenomenon.