Tolonium chloride (INN, also known as toluidine blue or TBO) is a phenothiazine that has been used as a hemostatic, a biological stain, and a dye for wool and silk. Tolonium chloride has also been used as a diagnostic aid for oral and gastric neoplasms and in the identification of the parathyroid gland in thyroid surgery. Toluidine blue has high affinity for acidic tissue components, thereby staining tissues rich in DNA and RNA. It has found wide applications both as vital staining in living tissues and as a special stain owing to its metachromatic property. Toluidine blue has been used in vivo to identify dysplasia and carcinoma of the oral cavity.

Evans Blue (EBD) is an azo dye which has a very high affinity for serum albumin. It can be useful in physiology in estimating the proportion of body water contained in blood plasma. Evans Blue Dye is widely used to study blood vessel and cellular membrane permeability as it is non-toxic, it can be administered as an intravital dye and it binds to serum albumin – using this as its transporter molecule. The EBD–albumin conjugate (EBA) can be: (i) identified macroscopically by the striking blue colour within tissue; (ii) observed by red auto-fluorescence in tissue sections examined by fluorescence microscopy; and (iii) assessed and quantified by spectrophotometry for serum samples, or homogenised tissue. has recently been utilised in mdx mice to identify permeable skeletal myofibres that have become damaged as a result of muscular dystrophy. EBD has the potential to be a useful vital stain of myofibre permeability in other models of skeletal muscle injury and membrane-associated fragility. Evans Blue is a potent inhibitor of L-glutamate uptake into synaptic vesicles. It also inhibits AMPA and kainate receptor-mediated currents (IC50 values are 220 and 150 nM respectively). P2X-selective purinoceptor antagonist.

Brilliant Blue is an organic compound classified as a blue triarylmethane dye. It is coal tar derivative food dye; used as the di-NH4 or di-Na salts. Coloring agent. Brilliant Blue FCF, has been used in foods in the US since 1929. This color adds a distinctive, bright blue hue to beverages, beverage powders, dairy products, baked goods, dessert powders, confections, condiments, icings, syrups, jams, jellies, marmalades, liqueurs, extracts, dairy fats and oil, meat, seafood, snacks, dry mixes and seasonings, fruit preparations, convenient food, and flavors. Both the diammonium and disodium salts of FD&C Blue No. 1 are used. The disodium salt is used in foods, while the diammonium salt has limited usage in drugs and cosmetics.

Patent Blue V (E-131) is a synthetic dye used as a food coloring. In Europe, it is used in beverages, preserves of red fruits, desserts, confectionary. In medicine, Patent Blue V is used as a contrast agent for visualizing lymphatic vessels. Patent Blue V is also used in dentistry in a disclosing tablet to demonstrate the presence of plaque on teeth.