This means that a tissue component stains a different color than the dye itself. For example, mast cell graules, cartilage, mucin, and amyloid will stain purple and not blue, which is helpful in identifying these components. Colonies appear as fuzzy blue clusters. Tissue gram stains are all basically the same as that used in the microbiology lab except that neutral red is used instead of safranin. The most sensitive method for demonstrating them is Methenamine silver.
Spirochetes are very difficult to stain.
The best method is the Warthin-Starry. A Giemsa stain may help demonstrate donovan bodies and leishmania. This stain uses carbol-fuchsin to stain the lipid walls of acid fast organisms such as M. tuberculosis. The most commonly used method is the Ziehl-Neelsen method, though there is also a Kinyoun's method. A modification of this stain is known as the Fite stain and has a weaker acid for supposedly more delicate M. leprae bacilli.