Why cyanosis does not occur in severe anemia?

Cyanosis refers to bluish color of the skin and mucous membranes which occur when the concentration of reduced hemoglobin is more than 5gm per cent. Patients suffering from severe anemia with hemoglobin content less than 5gram per cent may not show cyanosis as the total hemoglobin is less than 5 gram per cent. Ref: Textbook of Practical Physiology By G.K. and Pal, 2nd Edition, Page 127; Harrison's Principles of Internal Medicine, 16th Edition, Page 210; Fundamentals of Medical Physiology By Joel Michael, Page 50