RBCs, also called erythrocytes, have a protein called hemoglobin. The blood gets its color when hemoglobin absorbs oxygen from the lungs. As the blood travels through the body, the hemoglobin releases the oxygen in the tissues. RBCs have a life cycle of 4 months and they appear in the form of flat indented discs.
The WBCs, also called leukocytes, handle more complex functions. They are the defense mechanism of the human body for fighting infections. There are different types of WBCs with varied life cycles and distinct functions. White blood cells also produce a special protein called antibody which recognize and fight the presence of foreign elements in the body.