What is the difference in usage between amber and yellow, when it is the color of traffic lights or some derived meaning? Is this purely a difference between British English and American English, or does the context matter?
For example, on each side of the Pond, if you're driving, is it an amber light or a yellow light that announces an imminent red light? When indicating a status between red (no go) and green (ok), is the status amber or yellow?
EDIT: I already know that the UK has amber lights and the US have yellow light, this is not what I am asking here. What I am asking is whether there is more to it than a simple US/UK distinction. How unusual would it be to use the wrong word? Is the usage for traffic lights the same as for derived meanings such as traffic light rating system? What prompted this question was finding that the Wikipedia article on the rating system uses amber — I don't know if this reflects US usage as well, or if this is merely due to the article having been written by a BrE speaker, or if the RAG rating is a purely British notion and AmE speakers would not think to use a red/yellow/green rating system.