In a completed Gram stain,gram-negative bacteria are colorless.

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In a completed Gram stain, gram-negative bacteria will be pink/red in color due to the counterstain used after the primary stain is applied. The primary stain, crystal violet, will initially stain both gram-positive and gram-negative bacteria purple. However, during the decolorization step, gram-negative bacteria will lose the purple stain and take up the counterstain, which is usually safranin or basic fuchsin. This results in the gram-negative bacteria being pink/red in color.

In a Completed Gram Stain,gram-Negative Bacteria Are Colorless