Fast Blue RR Salt is widely used as a coupling agent in the production of azo dyes, which are essential for coloring textiles, leather, and paper. It is particularly valued in the textile industry for creating vibrant and durable colors on fabrics. Additionally, it is utilized in histology and biological staining processes to detect specific enzymes or cellular components, aiding in diagnostic and research applications. Its ability to form stable colored complexes makes it a key component in various analytical and industrial processes.