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Your blood is never blue, always shades of red.

When arterial blood leaves the lungs to circulate through the body, it has just a little bit more oxygen in it than does venous blood. The reason it appears bright red is that the combination of iron, oxygen, and hemoglobin absorbs higher energy wavelength light (blue and green) which leaves the red wavelengths available for our eyes to sense.

The venous blood is never blue, it is a darker color of red than arterial blood, not blue. The color is a burgundy red or maroon color. Blood is bright red in the arteries and dark red in the veins. The reason venous blood is a darker red can be partially attributed to the slightly less oxygen in the blood in the veins. But its color change is more due to the "waste" it carries away from the body tissues and back to the kidneys for filtering and elimination. This "waste" darkens the red color of the blood (think of it as a little like dirty dish water).

Although a popular belief, being in contact with air does not cause venous blood to instantly oxygenate and turn red. It is red outside the body because it is red inside the body as well. When you look at unopened veins inside the body, in endoscopy, for example, they are a dark red color.

The blue appearance of the veins that you see when looking at them through the skin is not caused by blue venous blood. As explained, that is always red. The blue appearance is caused by a reflective factor of the skin itself. It is an optical property of the reflection of light off light colored skin and the difference in that reflection from the veins under the skin (but near the surface). That reflective process is complex, but the blue-looking veins are mostly all about the skin and reflection.

If arteries were not too deep to be visible through the skin, then they, too, would have a blueish appearance, the same as the veins for the same reasons.

(See the related question below "Do humans have blue blood?" for a more in depth answer on the color of blood.)

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11y ago
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12y ago

Blood is blue when you are an animal that has copper in the blood, rather than iron. Horseshoe Crabs are one such animal.

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12y ago

when the oxygen is depleted

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Q: When is your blood red and when is your blood blue?
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Related questions

What gives oxygenated blood its blue color?

No deoxygenated blood is dark red and oxygenated blood is lightish red.


How whale have blue blood?

The colour of all whales' blood is red, not blue.


Is your blood blue or is it your veins?

Veins are blue because the blood is poor in oxygen, arteries are red because the blood is rich in oxygen.


What color is a persons blood?

red and blue. the red blood is closer to the other side of your skin and the blue blood is deeper in your body.


Why do you see red blood?

That's easy. When blood is in your body it is blue that's why your veins are blue. When oxygen meets the blood the blood turns red.


Why do you see red?

That's easy. When blood is in your body it is blue that's why your veins are blue. When oxygen meets the blood the blood turns red.


Is it true that blood is blue when it is not exposed?

No. Blood is bright red when it contains oxygen and dark red when there isn't a lot of oxygen. The blue you see in veins is the vein itself.


Does blood contain red blood cells and blue blood cells?

In relation to the human body, it is a common misconception that blood is blue; all blood is red. The blue appearance is due to the connective tissues of the blood vessels. Blood cells can be either erythrocytes, which are red, or leukocytes, which are white. When blood is oxygenated it is a much brighter red than de-oxygenated blood.


What color is blood going to the heart?

When the blood is going to the heart it is blue. When it is going away from the heart, it is red.


Is it true that all of the blood in your body is blue?

No. But the 'used' blood on its way back to the lungs is dull red, and looks blue through the veins.


What do blue lobsters eat?

The copper in their blood gives their blood a bluish tint. It is much like how iron in our blood causes our blood to be red. Haemoglobin is a red pigment in blood that makes the blood red when it comes out into oxygen (that why when we bleed, our blood is red.) some animals do not have haemoglobin in blood, for example LOBSTERS! So this is why their blood is blue.


Is blood really blue?

No, the blood is always red. The term,' blue blood' is given to noble people.