Tyrian Purple

Habacuc, his uncle and several other locals carried as many tortillas, and as much beans and coffee, as they could manage, along with large skeins of native cotton thread hand-spun on drop spindles by their wives, daughters and neighbors. After urinating in defense against the intrusion, snails release a milky, garlic-y scum that, pressed onto the cotton thread, changes, within minutes when exposed to bright sunlight, from yellow to green to blue, and finally to vibrant purple. Centuries later, Napoleon Bonaparte pined for an “imperial purple” porphyry tomb, but his envoys failed to find the ancient quarry; he had to settle for red.

Source: believermag.com