#1 Crystal violet is the primary stain, entering the cytoplasm and imparting a color to all cells that can be stained.
#2 Iodine complexes with the crystal violet within the cell, acting as a “mordant” to enhance the affinity of the cellular components for a dye.
#3 Acetone/alcohol removes the crystal violet-iodine complex from Gram-negative cells making them colorless.
#4 Safranin serves as a counterstain that imparts a pink color to the otherwise colorless Gram-negative cells.