It isn’t a misconception, deoxygenated blood is blue, when the oxygen in the blood had been used by the muscles the blood is the deoxygenated and blue until it is pumped to the lungs where is makes contact with oxygen which turns it red again. which is why when you get a cut blood is red… because of the oxygen in the air quote Bellion:

Wow, I can’t believe how many people believe blood is blue.

Blood is RED. Arterial blood is bright red. Venous blood is dark red. The color of blood is derived from its hemoglobin. Hemoglobin is red, either oxygenated or deoxygenated.

Veins are sometimes depicted in blue color in anatomy diagrams to make it easy to pick them out from the arteries. This often leads to the erroneous conclusion that venous blood is blue. Not true.

Another reason people think doxygenated or venous blood is blue is that veins can sometimes appear blue under the skin. Normal veins are actually mostly white or cream in color. The reason that veins observed through the skin and underlying soft tissue sometimes appear blue is that the skin and tissues preferentially absorb red light and mostly blue light is reflected back from the vein. Black lesions deep under the skin also will appear blue for the same reason, hence the term “Blue Nevus” for a mole that is located deep in the skin. Is the lightbulb inside of your brake light on your car red? Probably not, it’s white, it just has a red lens (filter) over it. What you’re actually seeing is the surface of the vein and not the blood inside. The walls of veins are opaque, you cannot see through the wall and therefore you cannot see the blood inside of them. Capillaries are thin enough to see through. Hold your hand up and shine a flashlight through it from the other side and you will see red. That is capillary blood you are observing. It’s red folks. If you see blue when you do this, your a crustacean.

RLJ