Red blood cells are the cells in the blood which carry oxygen and carbon dioxide through the bloodstream. They make up the majority of the solid portion of the blood - well over 95%. The red color is from hemoglobin, the actual molecule with a base of elemental iron that actually binds to oxygen and carbon dioxide and allows animals with bloodstreams to have cells that are not directly in contact with the environment in order to be oxygenated. Red blood cells are created in the bone marrow and destroyed by the spleen when they are damaged.