Final answer:
Gram-positive cells appear purple due to a thick peptidoglycan layer retaining the crystal violet dye, while Gram-negative cells appear pink after being stained by safranin. If Gram-positive cells appear pink, it is likely due to procedural errors in the Gram stain process, such as excessive decolorization.
Step-by-step explanation:
If Gram-positive cells lose their color and appear Gram-negative (too much pink), it is likely due to incorrect application of the Gram stain process. Gram-positive cells typically appear purple because they have a thick peptidoglycan layer in their cell wall that retains the crystal violet dye used in the staining process.
On the other hand, Gram-negative cells have a thinner peptidoglycan layer and do not retain the crystal violet dye after the decolorization step; instead, they appear pink because they are stained by the counterstain, safranin.
One common error that can cause Gram-positive cells to appear Gram-negative is leaving the decolorizer on for too long. This can result in the crystal violet dye being washed out of the thick peptidoglycan layer, making the cells appear pink instead of purple.
Therefore, cells that should be Gram-positive but look Gram-negative suggest procedural errors such as excessive decolorization.