The immature red cell containing a cytoplasmic network that stains with brilliant blue is called a reticulocyte.

Here's why:

* Reticulocytes are young red blood cells that have recently been released from the bone marrow.

* They still contain remnants of ribosomal RNA, which form a network within the cytoplasm.

* This network, called reticulum, is visible under a microscope when stained with a special dye like brilliant cresyl blue.

* This staining is used to measure the number of reticulocytes in the blood, which indicates the rate of red blood cell production.

Let me know if you'd like to learn more about reticulocytes!