Used as a biological stain in histology to visualize cell structures under the microscope, particularly in H&E (hematoxylin and eosin) staining where it colors cytoplasm and connective tissue pink or red. Commonly applied in pathology for tissue diagnosis and cancer detection. Also serves as a fluorescent tracer in some analytical applications and as an indicator dye in pH testing due to its color change properties. Widely used in ophthalmology to stain damaged corneal tissue for examination.