Why are arteries red?

Arteries are not actually red, they do however carry blood that is rich in oxygen making the blood red in color.

Arteries are not actually red in color. Arteries carry blood that is rich in oxygen. Oxygen attaches to the iron on hemoglobin found on Red Blood Cells. The oxidation of the iron on hemoglobin turns the blood red.

All arteries carry oxygenated blood away from the heart with one exception. The Pulmonary Artery carries blood rich in carbon dioxide from the heart to the lungs.

Veins which carry blood toward the heart. This blood is deoxygenated and rich in carbon dioxide which makes the blood take on a blue hue. The exception to this is the Pulmonary Vein which carries oxygenated blood back to the heart from the lung.