fabric colors that were “always” available to common man were shades of everything from red to blue, white, black, brown and grays. purple was also always available, but extremely expensive.
enter coal tar era of chemistry (starting 1840s or so): aniline and later diazo dyes made fabric in all possible colors not only available, but cheap. yes initially they sucked, they ran, they weren’t resistant to anything, they will give you ballsack cancer, but they were a thing. for a short time, purple fabric was a choice of the extravagant and the futuristic, and then people just stopped paying attention as it became more common
blue LEDs were sort of also used as a futuristic aesthetic choice, just after they appeared, but before these things became common, and now blue LEDs are just everywhere
Same thing happened to blue dyes. It used to be very expensive, but Prussian Blue being invented in the 18th Century made it show up everywhere cause it used to be so fancy, and then it just became a cheap dye.
Though the French loved that shit for government official and soldier uniforms, and supposedly that’s why cops wear blue