The color of blood smears can reflect severe underlying abnormalities in hematocrit and the presence of abnormal circulating immunoglobins.
The smear on the left, from a patient with polycythemia vera and a hemoglobin of 20 g/dL, appears noticeably darker than the normal (hemoglobin 14 g/dL) and pale anemic sample(hemoglobin 7).
The blood film on the right, from a case of myeloma, is blue because circulating monoclonal immunoglobins take up the basophilic stains used in blood smears.
Source: Wintrobe's Atlas of Clinical Hematology
blood smear
