ummm...they're not green in every country though, right? I think they are correct per country.
In Germany they are blue in iOS6. Which is sort of correct and true to life.
Well, actually just signs on the Autobahn are blue. Everything else outside of towns is a yellowish orange. Signs inside towns are just plain white. But even that is not the whole truth. What those signs really show is via which road you get to a destination, more or less. So if you are outside of town but not on a Autobahn a yellowish orange sign will have some town names on it and sometimes under the town names a white box with destinations inside that town (like a hospital or an airport).
Autobahn signs are a bit different. Since you will always travel on other roads to get to your destination when you leave the Autobahn town names are just on a blue background. Otherwise those Autobahn signs would be full of yellowish orange boxes. However, destinations inside town are still on a white background and the numbers of non-Autobahn roads you can reach via the Autobahn are yellowish orange.
Inside town you will see names of other towns on yellowish orange signs if you get there via some road outside the city that is not the Autobahn and on blue signs if you get there via the Autobahn. So actually even inside of town many signs are yellowish orange or blue. Just destinations inside of the town are white (library, town hall, whatever).
Oh, yeah, and street name signs are different from place to place. I have seen blue ones and white ones.
Munich, for example, is pretty well known for its blue street signs. Wikipedia tells me that there are apparently also red ones in Mainz. Street signs are much less standardised than all other road signs you will typically see in Germany (as is the case in many places in Europe).
Now, apart from me thinking that this is an interesting system this should also tell you something about Apples approach. Its skeumorphism is its downfall since Apple didnt manage to make something accurate at all. Its just gloss. Decoration. Not functional. Not even trying to be functional.
Im sorry, but plain white is better. Much better.
