[iopq]

Because they use 绿, not 青 so it would not result in blue lights

But in Korea they have the same confusion:

https://www.dreamstime.com/traffic-lights-road-blue-speed-li...

[the_mitsuhiko]

To the best of my knowledge it's different in Korea. As far as I know the call it blue lights but they are green.

[iopq]

They are not blue, but because the word for blue is also ambiguous they are more like a teal color