Fast Blue BB is primarily used as a dye in various staining techniques, particularly in histology and cytology. It is commonly employed in the visualization of tissues and cells under a microscope, aiding in the identification of specific structures or components. The dye is also utilized in biochemical assays to detect enzymatic activity, such as in the identification of phosphatases or esterases. Additionally, Fast Blue BB finds application in the development of colorimetric sensors and indicators, where it helps in detecting the presence of certain analytes through color changes. Its stability and reactivity make it a valuable tool in both research and diagnostic laboratories.