As a hematologist with a focus on blood disorders, I can provide some insights into the color of blood and its oxygenation levels.

Blood is composed of several components, including red blood cells (RBCs) which contain a protein called hemoglobin. Hemoglobin binds to oxygen in the lungs and releases it in the tissues. Oxygen-rich blood, or arterial blood, is typically a bright red color due to the high amount of oxygenated hemoglobin. On the other hand, oxygen-poor blood, or venous blood, is darker in color because it has less oxygenated hemoglobin.

The color blue is not typically associated with oxygen-poor blood. The misconception that blood is blue may stem from the fact that veins appear blue through the skin, but this is due to the way that light penetrates and is absorbed by the skin and blood, not the actual color of the blood itself. In reality, when you see a vein, what you're seeing is the blue color of the vein and the skin over it, not the blood inside.

So, to answer your question, oxygen-poor blood is not blue. It is darker red, and the blue color often associated with veins is a result of the optical properties of skin and veins, not the blood within them.

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Your blood is actually always red! Blood in your veins has very little oxygen and is a dark red color that looks almost blue when covered by your skin. Your arteries have bright red blood because it has a lot of oxygen in it that is being carried throughout your body to be used by tissues.read more >>