7. Blue blood
You must still remember all those illustrations in your textbooks where you saw how blood is delivered to the heart. There were red veins and blue blood vessels all over the human body. Nowadays only kids may believe that blood can be blue! The blue color that schemes show is used to demonstrate the difference in how blood flows. The fact is that blood is red regardless how it is delivered and where it flows. Blood can be dark red when it is deoxygenated.