indigo

Indigo is a deep, rich color that sits between blue and violet in many color systems. The term indigo also refers to a dye and pigment historically obtained from plants in the genus Indigofera, with indigo dye well known for coloring textiles blue. The word is derived from the Latin indicum meaning “from India,” reflecting its long association with Indian trade and production.

Indigo dye has a long history of use. It is produced from leaves of indigo-bearing plants such as Indigofera tinctoria and Isatis tinctoria (woad). Traditional production involves fermenting the leaves to release indican, then oxidizing to form indigo dye that is insoluble in water. The dye is used as a vat dye on natural fibers like cotton and wool. In the late 19th century, synthetic indigo was developed by Adolf von Baeyer, expanding supply and consistency, and synthetic indigo remains the dominant form in modern textile dyeing.

In color theory and color spaces, indigo is typically defined as the color between blue and violet. It is often said to be around 445 nanometers in wavelength if treated as a spectral color, but in practice indigo is not consistently treated as a distinct spectral color, and many color systems place it within or near blue. The CSS color named indigo is a fixed shade, usually represented as hex #4B0082.

Today indigo is used as a descriptive color in design, fashion, and branding, and as a historical reference to the dye and pigment in textiles. The term also appears in cultural and artistic contexts, sometimes overlapping with blue and violet in various palettes.