In Mayer mucicarmine staining, what color do the nuclei appear?

• A. Black
• B. Red
• C. Blue
• D. Green

Answer: (A)

Nuclei appear blue because Mayer mucicarmine uses a hematoxylin counterstain to color nucleic acids in the nucleus. This blue (often described as blue to blue-black depending on stain intensity) contrasts with the magenta/red staining of acidic mucins by the mucicarmine component. The combination lets you see mucin-rich areas in magenta while nuclei stand out in blue. If you ever see nuclei that look black, that usually indicates over-staining or overly aggressive differentiation, but under normal conditions the nuclei should be blue.