Comment by Macha

There's a few dyes (mostly pinks and cyans) that are outside sRGB space (though once you apply them to a material, that combination of material and dye might be fine), Tom Scott had a video a few years ago, though I don't know if that particular dye/seller is still going:

https://www.youtube.com/watch?v=_NzVmtbPOrM

There's also Vantablack and similar ultra-black dyes which are a somewhat adjacent phenomena but in the same category of "colors your screen can't display". The most black a pixel can be is "off" (and that's only achievable if the display is on if your screen is an OLED), and the back coating of your screen is probably not as black as those dyes.