Fast Green FCF 0.1% is used as a diagnostic tool in in vitro diagnostics. It is a solution consisting of true green FCF, a synthetic triphenylmethane dye, ultrapure water and a small amount of acetic acid. The solution is often used as a contrast agent in histology and is especially important in MILLIGAN trichrome staining. In this context, Fast Green FCF emphasizes the staining of collagen structures in tissue samples, creating a clear contrast with other tissue components. The acetic acid in the composition serves to regulate the pH of the solution, which improves the binding properties of the dye. Fast Green FCF 0.1% visualizes the structure and organization of collagen tissues in histological specimens.