In the polychromatophilic normoblast stage, the cytoplasm has begun to produce hemoglobin and, as a result, the color starts to shift from deep basophilic to a slate blue/gray shade. The cell continues to slowly shrink in size while the chromatin becomes much more knotted and clumped. The spoke-like pattern of the chromatin accentuates the nuclear membrane and the nuclear pores.
The top image on the right shows a clump of polychromatophilic normoblasts. Notice they are all very similar in size, shape, and stage of maturation. This is a classic pattern in erythroid development and these clusters are frequently associated with macrophages or histocytes in the marrow as they are the RBC precursors' source of iron. Note that the cytoplasm color is now a blue/gray rather than the deep midnight blue of the basophilic pronormoblast stage.
The lower image on the right shows a range of RBC precursors. At the bottom is a cluster of basophilic normoblasts (see red arrow), one of which is binucleate. There are also two cells above the cluster: the top cell is an early polychromatophilic normoblast (blue arrow), while the lower is a late basophilic normoblast (green arrow). Note the difference in cytoplasm color. The polychromatophilic normoblast is slate blue/gray, while the basophilic normoblast still maintains the midnight blue hue. Observe the nuclei and the chromatin pattern—the chromatin is much more condensed in the polychromatophilic normoblast.
