Indigo dye is a natural dye derived from the leaves of the Indigofera plant. It has been used for thousands of years to color textiles, producing a deep blue hue. The dyeing process involves fermenting the leaves to extract the indigo pigment, which can then be applied to fabrics like cotton and silk. Historically, indigo dye was highly valued in many cultures, including ancient Egypt and India. It played a significant role in trade and was often referred to as "blue gold." Today, indigo is still popular in fashion, especially in denim, and is also produced synthetically for various applications.