The presence of certain blue red blood cells (erythrocytes) seen in blood films stained with Romanovsky stains, as well as the normal pink cells. The cells that appear blue are juvenile erythrocytes.
Polychromasia, and polychromatophilia, are terms applied to an abnormal reaction of the red blood cells in severe anaemia. They have a bluish tinge instead of the normal red colour in a blood film stained by the usual method. It is a sign that the cell is not fully developed.