Used as a blue dye in the textile industry, particularly for dyeing cotton to produce denim fabric. Commonly employed as a pH indicator in analytical chemistry, showing color change in response to acidity or alkalinity. Utilized in medical diagnostics as a contrast agent during procedures like cystoscopy or angiography to visualize urinary or blood vessels. Applied in food industry as a coloring agent in certain products, approved in specific regions under regulated conditions. Serves as a redox indicator in titrations due to its reversible color change upon electron transfer. Used in biological staining to aid in microscopic examination of tissues and cells.