Younger locals who have mostly or only known the LED think it's a bit odd, but just call them blue because that's the common convention and many youths may think that the former lights might have actually been blue.

IIRC from when I moved to Japan the first time (30+ y ago) when the old lights were standard, being a wildly curious Gaijin enough to ask "why" about these kinds of strange contradictions, and having lots of exposure in that time to senior citizens who had the spare time and inclination to humor my incessant questions, several of these octogenarian to centarians remembered the introduction of the first gen traffic lights, when the automobile became common enough to require them; and this seeming contradiction was new; this was the explanation I have heard common across several distinct conversations in different towns:

1. 緑 "midori" as a character and word for green was not very common usage before the end of WWII.

2. The (pre-LED) lamps for all three were yellow bulbs viewed through glass filters that were 'red', 'clear-somewhat yellow', and 'blue' - so even though it may appear green, the blue was for the color of the glass.

Also because 青い "aoi" has persisted in use for certain shades of 'green' - for example green apples and leafy fresh veggies; so this 'blue' seems to match the actual color of the light and has an implicit meaning for Japanese - in the sense of 'go while light is still fresh' - and Japanese humor is primarily Punny instead of being actually Funny, so this double meaning resonates even after switching to truly green LED light sources.