Used as a biological stain in microscopy to enhance contrast in cells and tissues, particularly for visualizing nuclei and cytoplasmic structures. Commonly applied in histology and cytology for differential staining techniques. Also utilized in textile and paper industries for dyeing due to its strong affinity for cellulose and protein fibers. It provides a bright blue color with excellent fixation and wash-fastness, especially on silk, wool, and other protein fibers, making it popular for producing high-quality textiles.