My question Amber or yellow lights was closed as general reference. I do not understand why: what general reference?
The one reference that was cited in a comment is the Wikipedia article about the color amber. I do not see anything in it that would help answer the question. The article discusses some of the legal usage (which wasn't the focus of my question — if it had been, I would have wanted more information, but legal usage is fairly easy to research so I don't particularly care about it). The article can be said to mention that amber is British and yellow is American, though it isn't very clear — but a dictionary clarifies this. The basic UK/US distinction was mentioned in the question anyway: it was not what I was asking for.
I admit I hadn't mentioned my motivation for asking (why I thought there was more than a simple UK/US distinction) in the original question; I have now edited it. Nonetheless, I don't understand why even the original question was closed as general reference, considering that no general reference that I've seen goes beyond what I already mentioned in the question.