Why are arteries red and veins blue?

Since arteries are typically found at deeper levels of the skin, veins are the only blood vessels that are visible close to the skin's surface.

Because red and blue wavelengths absorb light differently, light incident upon skin tends to show veins as bluish, which is not reflective of the true color of the vessels.

Arterial blood appears brighter red within the vessels due to the erythrocytes' oxy-haemoglobin-containing pigment.

The oxygen has been removed from the blood in the veins, leaving the blood a deeper, almost maroon color.

Arteries and veins are distinguished in models and drawings by being colored red and blue, respectively.

Arteries appear red because they carry oxygen-rich blood away from the heart, while veins appear blue because they carry oxygen-depleted blood back to the heart. The perception of veins as blue is due to the way light interacts with the skin and the blood vessels beneath it.