Blood Agar: This type of differential media differentiates organisms on their ability to lyse red blood cells (hemolysis) through the production of the extracellular enzyme hemolysin.

β-hemolytic activity (A) will show lysis and complete digestion of red blood cell contents surrounding colony. e.g. Streptococcus haemolyticus.

α-hemolysis (B) will only partially lyse (the cells are either lysed or not- it is the digestion that may be incomplete) the hemoglobin and will appear green. e.g. Streptococcus viridans.

γ-hemolysis (C) is the term referring to a lack of hemolytic activity. 

Extravascular hemolysis

Occurs at either the liver or the spleen, where there is a higher level of white cells. The hint for this is a positive direct anti globulin test (Coombs test)