[1] Using multiple stains can better differentiate between different microorganisms or structures/cellular components of a single organism.
The process or results are called a WBC differential.
This test is useful because many diseases alter the proportion of certain white blood cells.
By analyzing these differences in combination with a clinical exam and other lab tests, medical professionals can diagnose disease.
Gram staining uses two dyes: Crystal violet and Fuchsin or Safranin (the counterstain) to differentiate between Gram-positive bacteria (large Peptidoglycan layer on outer surface of cell) and Gram-negative bacteria.