Amber or yellow lights

Question

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?

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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.

Answer 1

I'm not sure I've ever heard of yellow traffic lights, but here are 65 written instances of "drove through a yellow light".

I assume it's a US/UK difference. To my British ear, "drove through an amber light" sounds natural, but there are actually only 7 of them.

Note that "ran a yellow light" gets 369 hits, against 23 for "ran an amber light". That stronger bias I put down to the fact that ran a red light is about ten times more common in the US than the UK.

I doubt anyone's choice of colour-word would be influenced by the exact wavelength/frequency of the lights themselves on either side of the Atlantic, but it's worth noting that the UK sequence is Red, Red and Amber, Green, Amber, whereas in the US it's just Red, Green, Yellow. The colour amber is often described as a reddish or brownish yellow. Perhaps British usage is influenced by the fact that half of all the times we see our "yellow" light, the red one is also on.

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The official British "security alert" scale was headed by red, amber until it was replaced in 2006 (by an apparently non-colour-coded scale). The American equivalent has red, orange (yellow next).

Answer 2

For what it's worth, in the US military, the status of things like communications, logistics, or tasks are referred to as Green / Amber / Red. For some reason, with that background, I call the lights on a stop light Green / Yellow / Red but any similar status updates in the civilian world I still use Green / Amber / Red.