Fast Blue Substrate (20 mL Blue Buffer + 420 uL each Blue Reagents 1-3) is an individual component of the ViewRNA™ ISH Tissue Assay Kits, 2-Plex, 24 assays (Cat. No. QVT0012). It is a blue precipitating substrate with components 1 -3 used for the detection of alkaline phosphatase activity.