In this protocol, what color change indicates metachromasia?

• A. Rose-red
• B. Blue
• C. Green
• D. Purple

Answer: (A)

Metachromasia happens when a basic dye binds to certain tissue components and shifts color from its ordinary stain color to a different hue. In this protocol, that metachromatic shift appears as rose-red, so seeing rose-red indicates the metachromatic reaction has occurred. This happens because tissue elements like sulfated glycosaminoglycans alter how the dye aggregates, changing the light absorbed and thus the color observed. The normal dye color (blue) would not indicate metachromasia, and green isn’t the expected metachromatic result for this staining system; purple can occur in some variants, but the protocol here yields rose-red as the metachromatic indicator.