What is the purpose of neutral red stain in gram stains?

Neutral red stain is used in Gram staining as a counterstain to differentiate Gram-negative bacteria from Gram-positive bacteria. After the primary crystal violet stain and the iodine mordant, the slide is decolorized, which removes the crystal violet from Gram-negative bacteria. The neutral red then stains these decolorized Gram-negative cells, allowing for clear visualization under a microscope, while Gram-positive bacteria retain the crystal violet color. This provides a contrast that aids in identifying bacterial types based on their cell wall characteristics.