Gram stains go in which color tube?

• A. Blue Tube
• B. Red Tube
• C. Green Tube
• D. Yellow Tube

Answer: (B)

Lab color-coding helps you identify which tube to use for a given test, and Gram staining is assigned to the red-top tube in this system. The Gram stain differentiates bacteria by cell wall properties, with Gram-positive appearing purple and Gram-negative taking on a pink/red color after counterstaining. In this protocol, the Gram-stain reagents and steps are designated to the red-top tube, so red is the correct choice. Other colored tubes are reserved for different tests or reagents, so they aren’t used for Gram staining.