The Periodic Acid-Schiff (PAS) – Alcian Blue Stain Kit is a powerful combo stain used in histology to differentiate between acidic mucins as sialomucins, sulfomucin and neutral epithelial mucin. After staining, acidic mucins will be coloured blue, neutral in magenta and nuclei in deep blue. Mixtures of acidic and neutral mucins give blue/ purple colour.