does protein produce hemoglobin
Each hemoglobin protein is made up subunits called hemes, which are what give blood its red color. More specifically, the hemes can bind iron molecules, and these iron molecules bind oxygen. The blood cells are red because of the interaction between iron and oxygen. When the iron is oxygenated(Fe+3), it becomes red. When the iron is deoxygenated(Fe+2), it becomes blue. This is why your veins are blue. When hemoglobin is carrying a lot of oxygen (like when just leaving the lungs), blood is bright red.