Pigments are chemicals. Chemist can use various techniques to analyse a sample and tell what is its composition. After that they search for it in the literature and if they find that the given chemical was not described previously then it is novel. That’s it.

> I don’t get it, how would you even discover a pigment?

The article answers this. “ Chemist Mas Subramanian and his team serendipitously came upon it while conducting experiments with rare earth elements as part of their work with semiconductors.”

That is to say they were experimenting and something turned out as blue. They didn’t expect this so they analyzed the sample and then did a literature search.

I suspect it starts with "this compound has a nice colour, how about its other properties?"

How would you know what you’re looking at is novel?

There are extensive lists of existing pigments.

It wasn't that long ago that a blue pigment—anything at all that was blue and that would be durable over time—was extraordinarily rare and valuable.