Red pigment in red blood cells?

The red pigment in red blood cells is called haemoglobin. Haemoglobin is an iron-containing protein that is responsible for carrying oxygen from the lungs to the rest of the body. It is made up of four protein subunits, each of which contains an iron ion. When haemoglobin binds to oxygen, it changes colour from red to bright red. This change in colour is what gives blood its red colour.