Indigo is a deep blue-purple color that sits between blue and violet, like the color of the sky just after sunset or a really dark pair of jeans. The word also refers to the plant that produces this rich, distinctive dye.

For thousands of years, people extracted indigo dye from the leaves of indigo plants, creating one of the most valued colors in textile history. Making indigo dye required skill and patience: workers fermented the leaves in water, then oxidized the liquid to create the deep blue pigment. The process was so labor-intensive that indigo-dyed cloth became a luxury item, worn by wealthy people and royalty across Asia, Africa, and eventually Europe.

Indigo became especially important in India, where artisans perfected the dyeing process and created beautiful indigo-dyed fabrics for centuries. British colonizers later forced Indian farmers to grow indigo instead of food crops, contributing to terrible famines. When synthetic indigo was invented in the 1890s, it replaced natural indigo in most manufacturing. Today, that synthetic indigo dye colors almost every pair of blue jeans in the world.

You might remember indigo as one of the seven colors in the rainbow, though many people debate whether it's distinct enough from blue and violet to deserve its own spot.