Synonyms for the term "vat dye" include indigo, woad, and Tyrian purple. Vat dyes are a type of dye that are dissolved in a reducing agent before being applied to the fabric substrate. They are highly versatile, and can produce a range of colors, from blues and greens to purples and browns. Vat dyes are very resistant to fading, and are commonly used in denim and other durable fabrics. The term "vat" refers to the large containers often used to mix and store the dye. As a result, vat dyes can also be referred to as dip dyes or immersion dyes.