Amber or yellow lights

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.

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).

Amber and yellow are two different colors, technically.

Yellow is one of the CMYK primaries (0,0,100,0), while amber has a bit of magenta in it (0,25,100,0). On the color wheel yellow is at hue 30 and amber at 45. RGB values are 255,0,0 for yellow and 255,191,0 for amber.

In LCH space, which encodes perceptual brightness (L), chroma (C, richness) and hue (H), you can see that yellow is brighter than amber (L=97 vs L=81) and richer (C=86 vs C=57).

It turns out that there is a different definition of amber (SAE/ECE amber) when it comes to turning lights for cars. This amber is at RGB 255,126,0 which puts it even darker (L=66) and murkier (C=29) than the amber defined above.

There are some car lights that are strongly yellow (fog lamps). For these selective yellow is used.

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.