Many people believe that that deoxygenated blood is blue, but this is not the case; human blood is red both inside and outside the body. There are several reasons why people believe that blood is blue, including the fact that veins appear blue under the skin and that some biology books illustrate the circulatory system with blue veins and red arteries. All human blood, however, is red, because it gets its color from red blood cells, which contain iron.
More about the color of blood:
- Both venous and arterial blood is red, but arterial blood is brighter in color, and venous blood is darker. This can have some effect on the appearance of veins, making them appear to be blue.
- Male cockroaches have colorless blood, and some adult female roaches have orange-tinged blood.
- The term "blue blood" is sometimes used to describe people of aristocratic birth. One explanation for the term is that highborn people would not be tanned as a consequence of outdoor labor. As a result, their blue veins would show more prominently under their fair skin.