In Ballad of the White Horse, G.K. Chesterton describes the Virgin Mary:

Her face was like an open word When brave men speak and choose, The very colours of her coat Were better than good news.

Why the colors of her coat?

The medievals took their dyes very seriously. This was before modern chemistry, so you had to try hard if you wanted good colors. Try hard they did; they famously used literal gold, hammered into ultrathin sheets, to make golden highlights.

Blue was another tough one. You could do mediocre, half-faded blues with azurite. But if you wanted perfect blue, the color of the heavens on a clear evening, you needed ultramarine.

Here is the process for getting ultramarine. First, go to Afghanistan. Keep in mind, you start in England or France or wherever. Afghanistan is four thousand miles away. Your path takes you through tall mountains, burning deserts, and several dozen Muslim countries that are still pissed about the whole Crusades thing. Still alive? After you arrive, climb 7,000 feet in the mountains of Kuran Wa Munjan until you reach the mines of Sar-i-Sang. There, in a freezing desert, the wretched of the earth work themselves to an early grave breaking apart the rocks of Badakhshan to produce a few hundred kilograms per year of blue stone - the only lapis lazuli production in the known world.

Buy the stone and retrace your path through the burning deserts and vengeful Muslims until you’re back in England or France or wherever. Still alive? That was the easy part. Now you need to go through a chemical extraction process that makes the Philosopher's Stone look like freshman chem lab. "The lengthy process of pulverization, sifting, and washing to produce ultramarine makes the natural pigment … roughly ten times more expensive than the stone it came from."

Finally you have ultramarine! How much? I can’t find good numbers, but Claude estimates that the ultramarine production of all of medieval Europe was around the order of 30 kg per year - not enough to paint a medium-sized wall. Ultramarine had to be saved for ultra-high-value applications.

In practice, the medievals converged on a single use case - painting the Virgin Mary’s coat.

https://www.astralcodexten.com/p/the-colors-of-her-coat