Which term describes the rose-red staining observed in this protocol?

• A. Metachromatic
• B. Basophilic
• C. Eosinophilic
• D. Anisotropic

Answer: (A)

Metachromasia is at work here. Some dyes, like toluidine blue, normally stain tissue blue, but when they bind to certain substances—notably the highly sulfated glycosaminoglycans packed in mast cell granules—the dye undergoes a color shift and appears rose-red or purple. That color change is the hallmark of metachromasia, indicating the presence of those specific substrates. Basophilic staining simply means components bind a basic dye and typically look blue; eosinophilic staining refers to affinity for acidic dyes, giving pink to red; anisotropic describes how some structures show birefringence under polarized light, not a color change from dye binding.