Is human blood blue?

No, human blood is not blue. The misconception that blood is blue comes from the fact that veins often appear blue through the skin. However, blood is never actually blue when it's inside the body.

The reason veins might appear blue is due to the way light interacts with skin and tissue. Blood in veins appears blue to the human eye because of the way light is absorbed and scattered by the skin and tissues. When light passes through the skin, the shorter wavelengths (such as blue) are absorbed more readily by the tissues than the longer wavelengths (such as red). This selective absorption and scattering can make the veins appear blue.

However, blood itself is always red, due to the presence of hemoglobin, a protein in red blood cells that binds to oxygen and gives blood its red color. Even when blood is deoxygenated and has a darker red or purplish hue, it's still not blue.