A set of two stains that are used to stain (crystal violet and iodine) and counterstain (fuchsin) bacteria. gram-negative bacteria are completely decolorized after treating the stained bacteria with ethanol or acetone and can be visualized by the counterstain. They have a complex cell wall in which the peptidoglycan layer is covered by lipopolysaccharides in an outer membrane structure. gram-positive bacteria resist decolorization by ethanol or acetone, they retain the initial gram stain. They have a cell wall consisting predominantly of peptidoglycan not overlayed by an outer membrane.