Final answer:
After the Gram staining process, Gram-negative bacteria exhibit a pink or red color due to their thin cell walls and outer membrane that only retains the safranin counterstain.
Step-by-step explanation:
The classification of bacteria based on the Gram staining technique involves differentiating them by the color they exhibit after the staining process. Gram-negative bacteria stain a pink or red color. This is because the cell walls of Gram-negative bacteria are thinner and possess an outer membrane that does not retain the crystal violet stain used during the Gram stain method. Instead, they are counterstained with safranin, resulting in a pink appearance under the microscope.