Green was hard to make and harder to keep. The dye wouldn’t hold — it faded, it shifted, it wouldn’t sit still on cloth — and medieval guilds kept the blue dyers and the yellow dyers separate by law, so you couldn’t just mix your way to it. Pastoureau’s argument is that the chemistry became the meaning. If the color won’t stay put, it gets attached to everything else that won’t: luck, chance, gambling, money, youth, love, fate. And then to poison, the devil, and treachery. He runs it from the Greeks, who may not have had a word for it, through Nero, through Islam adopting it, through Goethe calling it middle class and Kandinsky calling it dull, to the reversal nobody saw coming, where the least trustworthy color on the wheel became the one that means save the planet.