Under http://wiki.answers.com/Q/What_are_some_strange_things_about_Japan, I found this interesting tidbit:
The words for green and blue are the same in Japanese (unless you're referring to plants), so the word for green traffic lights is "blue."
That's not right. At least not entirely. The explanation is far too simple and, if this was all you ever saw on the subject, you would have a warped opinion on the 'ignorant' Japanese in much the same way that people have about Canadians.
Re: Canadians. We have a professional football league called the Canadian Football League (CFL) that has a field 10 yards longer (110 x 65 yards) than a U.S. one (100' x 53-1/3 yards), have 20 yard deep end zones compared to 10 yard deep ones for the U.S., has only three downs as opposed to the U.S. four, Canada uses 12 men compared to the U.S. 11. As well, when the CFL had nine teams up until a few years ago, two of the team nicknames were Rough Riders. Well, actually, one of them was known as the Roughriders. We also have a team called the Eskimoes, which is politically incorrect, as Eskimoes are known as Inuit... the only equivalent I can think of is someone calling their team the Redskins. Oops.
Anyhow... back to Japan and the whole green-blue thing.
Green = Midori
Blue = Ao (pronounced 'ow')
The word 'midori' is actually a relatively new thing in the Japanese alphabet. New being relative, as it first appeared sometime in the Heian-jidai (Heian era) of 794-1185AD... so 1200 years ago or so...
Before that (and even after that), the kanji used for Ao could be used for green and for blue, as the Japanese at the time seemed to think that green was a variation of blue. Obviously Japan needs to stop allowing people with trouble differentiating colors NAME the colors!
This is the kanji for Ao: (青, n., aoi (青い, adj.)
There is no reason for any discrepancy between colors to still exist in 2013, but it does. Apparently the word 'Ao' can still be used when describing vegetables, fruits and plants. It is not used as such when the color is obviously green when describing such things as a green car, a green LEGO brick or green bikini.
But... for some reason, even though it makes no sense to me, Japan uses the word Ao when describing traffic lights.
"The light is blue, Suzuki-san. Let's go!"
If you said that the light is green, you might give yourself away as being a gaijin to Suzuki-san. You might always get a rap on the back of tyhe head which might cause you to yell 'ao' in pain.
Anyhow... I hope that clears things up. The Wiki Answers are sort of correct, but not in the correct sense.
PS: That photo up above is from Wikipedia: A billboard in Okazaki, Aichi, depicting traffic lights with a blue, rather than green, 'go' signal. The distinction of blue and green in Japanese is fluid enough to allow these variances in the depiction of the color.
The photo is part of a larger photo taken by Garrett Albright.
Original photo below: