Used as a direct (textile) dye for cotton and paper due to its strong affinity for cellulose materials. Commonly applied in histology as a diagnostic stain for amyloid deposits in tissues, where it produces characteristic apple-green birefringence under polarized light. Employed in analytical chemistry as a pH indicator, changing color from blue to red in the pH range of 3.0 to 5.0. Also utilized in research to study protein aggregation and fibril formation, particularly in neurodegenerative disease models.