Azure, a methylated thiazine dye, is a metachromatic basic dye indicator which is resulting and ranging from green (to chromosomes) and blue (to nucleoli and cytoplasmic ribosomes), to red colour (to deposits containing mucopolysaccharides). There are many methylated homologues used as components of many polychrome stains in combination with eosin and methylene blue in pH adjusted solutions.

Azure Dye - Classified in following category:
 

Azure A: Also called Methylene Azur A asymmetrical Dimethyl Thionine a dye used in nuclear and blood stain. Azure A CAS No is 531-53-3.

Azure B also called Methylene Azur B Trimethylthionine chloride a dye used in biological stain a component of polychrome Giemsa's stain for blood protozoa. Used for staining semi-thin sections of plant tissue. Azure B CAS No is 531-55-5

Azure C: Mono Methyl Thionine chloride used in staining of mucins and cartilage.

Azur II : a mixture of azure B (azure I) and methylene blue in equal amounts. Its classified CAS No is  37247-10-2

Azuresin: a complex of azure A and carbacrylic cationic exchange resin, used as a diagnostic aid in the detection of gastric achlorhydria without intubation. (Azure is the name of blue colour between blue and cyan like sky colour on a clear day.)