Why do blood vessels look blue under the skin?

Blood in the arteries is bright red, blood in the veins is dark red mostly from the impurities that are being carried back to the kidneys and liver for disposal that are mixed in and brownish which darkens the red color to more maroon. Blood in veins can look "blue" when viewed through the skin because of light refraction and other factors. But the blood is red and the veins are actually white.When a person donates blood, it comes from a vein, not an artery. It is also not exposed to air, or it would be contaminated and need to be disposed of. It also happens to be dark red, NOT blue.The common misconception of "blue" blood is continued due to textbook illustrators use of blue and red to differentiate arteries and veins. Venous blood is actually a burgundy or maroon color.

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1)Skin absorbs blue light.-----Subcutaneous fat only allows blue light to penetrate skin all the way to veins, so this is the color that is reflected back. Less energetic, warmer colors are absorbed by skin before they can travel that far. Blood also absorbs light, so blood vessels appear dark. Arteries have muscular walls, rather than thin walls like veins, but they likely would appear the same color if they were visible through the skin.2)Deoxygenated blood is dark red.-----Most veins carry deoxygenated blood, which is a darker color than oxygenated blood. The deep color of blood makes veins appear dark, too.3)Different sizes of vessels appear different colors.------If you look closely at your veins, for example, along the inside of your wrist, you'll see your veins are not all the same color. The diameter and thickness of the walls of the veins plays a part in the way light is absorbed and how much blood is seen through the vessel.4)Vein color depends on your perception.-----In part, you see veins as more blue than they really are because your brain compares the color of the blood vessel against the brighter and warmer tone of your skin.
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It is an optical illusion caused by light reflecting on and through the skin.Blood in the arteries is bright red, blood in the veins is dark red mostly from the impurities that are being carried back to the kidneys and liver for disposal that are mixed in and brownish which darkens the red color to more maroon. Blood in veins can look "blue" when viewed through the skin because of light refraction and other factors. But the blood is red and the veins are actually white

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The blood in your veins is called venous blood.What colour is venous blood?When the haemoglobin in your blood combines with oxygen it turns bright red. When it loses oxygen it turns dark red. It may be described as dark crimson which reflects some blue but not enough to make it look blue or purple.I have taken blood samples from veins many times and have donated blood many times and it always comes out of the vein as a very dark red colour. I have seen many blood agar plates kept in conditions where there is no oxygen--and the plates are dark red. I have taken blood with a vacuum syringe which contains no air at all. I have never seen the blood inside the syringe look blue.Some people think that blood comes out of the vein and immediately turns red because it comes into contact with oxygen. When you watch blood coming out of your arm into a transparent tube, you realise that it is not contacting oxygen and it is a very dark red. In low light it almost looks black. When I first saw a bag of blood at the Red Cross I didn't recognise it at first because it was so dark red.So why does the dark red blood look blue when it is in the veins? Veins are white, so the colour of the veins is not the reason.It's because the light from the sun and light globes, etc is made up of many different colours and these are absorbed at different rates the deeper you go through the skin.It's like what happens underwater...I have been scuba diving and the deeper you go the less red you see unless you take a light with you. Everything looks blue, green or black. The water is absorbing the red end of the spectrum so that only blue light remains to be reflected. When you look into a deep swiming pool with a white bottom, it appears blue. Apparently skin does the same thing to the light. The deeper under the skin you go the bluer things look.Then why does the skin of pale-skinned people turn red when they blush or become flushed? The tiny capillaries which carry the blood are so close to the surface of the skin that none of the red colour is filtered out.But the blood in the veins which are a little further in under the skin look blue. Although it is really dark red!

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