Neutral red acts as a pH indicator, changing from red to yellow between pH 6.8 and 8.0.  A vital dye used as an indicator and biological stain. Various adverse effects have been observed in biological systems.

Application

Neutral red is a eurhodin dye used for staining in histology. It stains lysosomes red. It is used as a general stain in histology, as a counterstain in combination with other dyes, for many staining methods. Together with Janus Green B, it is used to stain embryonal tissues and supravital staining of blood.