Learn how to use this product Trypan Blue Stain is a dye used to assess cell viability. Trypan Blue can't stain cells with an intact cell membrane, meaning that live cells remain colorless and the nonviable are stained blue. Trypan Blue stain 0.4% can be used for brightfield cell counting and is compatible with LUNA-II™, LUNA-FL™, and LUNA-FX7™ automated cell counters, and the CELENA® S Digital Imaging System.