@kdfrawg The big paint producers all put pigment numbers on the tubes, and because lots of people use them, there are real world reports of how they perform. The small ones are more of a gamble, though they might provide information if you ask.
For work that’s to be photographed, or that will live in a sketchbook, the lightfastness doesn’t matter, but it does for work that will be on display. I don’t need mine to last for hundreds of years, but if I like something, I’d hope to be able to keep it stable for my lifetime, which might reasonably be several decades.
// @streakmachine