Metachromatic granules are referred to as the volutin granules because of the reaction of these granules with the dye which helps in visualizing them under the microscope.
Metachromatic are the intracytoplasmic granules which are used for storing the inorganic polyphosphate.
These large inclusion bodies can be generally seen in the bacteria.
These granules could be said as metachromatic as they can take a colour different from that of the dye. For an instance, metachromatic granules will stain pink with methylene blue.