Reticulocytes are the excessive cells between late juvenile erythrocytes and fully mature erythrocytes, due to the basophilic RNA material still present in their cytoplasm, after live staining with Brilliant Tar Blue Staining Solution, light or dark blue reticulocyte structure can be seen in cytoplasm by microscopic examination.

Brilliant tar blue staining solution is mostly used for live staining of reticulocytes, and the background color of the results stained with this staining solution is bright and clear, and it is not affected by prolonged over-staining.