Amber is one of the few colour terms in the palette named after a specific material rather than a plant, an animal or an ore, and the material had a life of its own long before the colour word settled.
Amber is fossil tree resin, tens of millions of years old, and the great European source is the Baltic coast. It was traded south along routes documented from the Bronze Age onward, reaching the Mediterranean in quantity, and Baltic amber has been recovered from graves and hoards across the length of that trade. It was worked into beads and amulets, it sometimes contains trapped insects, and it burns with a resinous smell, all of which contributed to it being treated as a substance with properties rather than merely a pretty stone.
One of those properties turned out to matter enormously. Rubbed amber attracts light objects, an effect the Greeks noticed and attributed to the material they called elektron. When William Gilbert came to name the phenomenon in 1600 he took it from the Greek word, and electricity is therefore named after the colour of fossil resin.
As a pigment the colour was got from ochres and from resinous varnishes, and amber itself was dissolved into varnish recipes, though the resulting medium is dark and difficult. The modern use of the word for traffic signals and for warning lights is a twentieth century convention that has no connection to the earlier associations at all, and it is now the sense most English speakers reach for first.