Is Blood Ever Blue? Science Teachers Want to Know!

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According to one of the leading experts on the human circulatory system, blood flowing through veins is blue.

I’m not going to mention any names. All I’ll say is this: A person I know visited a major research center last year and saw a demonstration of organ removal and some other experimental stuff. A person also visiting asked the famous high-level researcher doing this work if blood was ever blue. What he said was not recorded in detail, but it was very much like this statement I found on the Internet:

… human blood is red as soon as it is oxygenated. Blue blood flows through veins back to the heart and lungs…..
[source: Some Guy on Yahoo Answers]

My friend was disturbed by this, as s/he had been teaching high school students for years that blood is not blue. Her understanding of the situation was that people thought blood was blue because standard anatomical drawings and models depict arteries as red and veins as blue, and because if you look at your veins they are blue. Obviously veins are not clear, but if you don’t think that out you might assume that you were seeing blue blood.

So another year goes by and the same thing happens again. Another visit to the operating theatre, another person asks about blue blood, another confirmation that blood is blue.

Now, I’ve seen both veins and arterial blood either seeping or gushing (respectively) out of various organisms, including humans and various other mammals, on a number of occasions. My grandmother used to spurt out blood now and then because of a condition she had. As I study hunting, I’ve observed lots of thrashing around blood spurting and seeping mammals. I’ve cut myself and I’ve donated blood. And so on.

I’ve never seen blue blood. I’ve seen darker red and lighter red blood. But never blue.

Now, going back to Yahoo Answers, which I am NOT recommending as a source for actual information, but which is a good source for what regular people sometimes think, we have the following three quotes:

Melissa says: When blood gets oxygen it turns red but in your veins it is blue just look at them.

Avondro says: Myth, it’s always red. It goes a darker red, purple-like (Some call it blue) when starved of Oxygen.

SS Agent Dick Wakka says: Somewhat true. Blood is very bright red when it is in the pulmonary vein in the lungs, when it is highly oxygenated. During it’s journey back to the heart after circulating through the body, it is a little blue when it is deoxygenated, but more of a maroon-blue mix. … This is the truth.

Agent Dick gives as a citation a “medical student.” Well, I’ve got a citation of a leading blood researcher at a major research institution that says blood is blue.

I think there are two things going on here, one having to do with physics and the other with culture.

The physical issue is about color. Is “purple” a kind of red, or is it a kind of blue? Beyond that, is blood that is “dark red” or “purple” really purple? Or is it dark red. See my point?

The cultural issue is that more surgeons and folks like that, for much of recent history, are males, and males are bad at color, on average. I’m not talking about color blindness, but rather, color indifference.

So here is what I think: If a person who says to themselves “Blood is blue in our veins” thinks either of the following:

… That blood is blue, like this:

… Or, that blood is “blue” in that you look at your veins and see blue, thus you are seeing your blue blood….

… Or, that you look at an anatomical chart and see the veins drawn in as blue, therefore the blood inside them is blue…

… then that person is laboring under a misconception.

If a person thinks that this “blue blood” is purple, then they may also be laboring under a misconception. The HTML Internet Purple looks like this:

(I know, it looks dark blue to me as well.)

And the Pantone purple looks like this:

(I’ve never seen blood that looks like this)

Pantone Dark Red looks like this:

… but not very much like the darker shades of blood that I’ve seen.

I think dark blood looks a little like this:

This color is 24% red, 2% green, 2% blue, but at a saturation of 92 with a color value of 24 and a hue of 0 degrees. Whatever that means.

(By the way if your computer’s video display is not set to a high value for number of colors shown, all of the above may look like only one or two colors. And, since all video screens are different, I might be seeing something different than you are…)

Anyway, the color that I personally think resembles blood in its darker state is not purple. It is red with a lot of darkness added to it. Or a lack of lightness, or whatever. But it is red.

Human, mammal, and many other organism’s blood is red. But finding out if this is “true” is like squeezing blood from a stone.

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11 thoughts on “Is Blood Ever Blue? Science Teachers Want to Know!

  1. The best thing to do is to ask a phlebotomist.

    Back in another life as a medical researcher I used to bleed lab colleagues for (amongst many other things) leucocytes to be used as feeder cells, and for plasma for various haemostasis assay controls. We bled from the cephalic and medial cubital veins into various stoppered glass tubes with all sorts of anticoagulants, and also into polystyrene universal tubes with glass beaks that were shaken until the clotting proteins coagulated around the beads.

    Blood comes out of a vein as a colour probably somewhere between the last two samples in the OP. If you’ve ever nicked a vein and seen that dark red colour, that’s venous (deoxygentated) blood. Arterial blood is definitely a brighter red (some say cherry red, but dark cherries are like venous blood!), and deoxygentated blood can be oxygenated in a petri dish to become more brightly red, but one way or another all human is red. For that matter, all blood from the dozens of different mammal, bird, herp, and fish species that I’ve bled has been pretty much the same colour as human blood.

    The blue colour of veins is an optical phenomenon resulting from the way that light reflects and refracts from/through the vein walls and through the overlying tissue. People refer to the aristocracy as “blue bloods” because in older European times the wealthy tended to spend more time indoors and/or covered when they went outdoors, and thus had paler skin than the peasant class. The paler the skin, the more obvious is the blueness of surface veins – but it has nothing to do with the actual colour of blood, beyond how the dark red colour contributes to the optical phenomena that filter reflected light back out through human skin/tissue.

  2. I was curious so I asked a nurse. (I think I was in for day surgery.) She said, arterial blood is sometimes almost bright pink.
    A note about purple, the “royal purple” distilled from an eastern Mediterranean snail, used to dye the wool of royalty and the edge of the robes of the Roman senators, _Murex sp.:_ it sometimes came out a bright red, though presumably on the crimson side. I have read that cloth died with murex purple had an awful stink. I have had a dealing with rotting whelks so it did not surprise me. It may have added to the taboo of kingship.
    The word purple is often used interchangeably with violet, but it is the redder hued variety, on the magenta and fuchsia side.

    1. David, thanks for the comment. Great to have an expert on ancient colors such as yourself weigh in.

      Interesting to consider the possibility that early color terms were for the process, which produced what we see today as a range of colors, rather than the actual color.

      Also, as it widely but not accurately known, different cultures have different levels of intensity of naming colors. The Efe with whom I lived had white, black red, and green. Things that were lightish of any color where white, things that were darkish of any color were black, and certain things that were red or green were called, sometimes, red or green.

      In other words, they were like me … not color blind but somewhat color indifferent. In a world where all things are natural (almost) color is usually not a useful attribute. Anything with a bright yellow, reddish, or orange color (meaning a warning of venom or toxin, like in a toad stool) are red to them. That’s all they need.

      No Efe would ever say, “you know that one plant, with darker brown bark and light yellowish red leaves with the white stripes?” …. they would simply name the species. Using color to describe their environment is roughly like a car lover using color to describe model-make of cars.

      (this might make a good blog post some day)

      And yes, I know the smell of a rotten whelk.

    2. This reminds of a book that i strongly recommend about the colour mauve and its history. It played a fair part in the development of modern industrial chemistry.
      I think it was called Mauve, the colour that changed the world; or something similar. Really entertaining read it was.

  3. Just for fun, search ‘cyanotic definition’ (or something similar) in Google images. Reminds me of the old days when swim instructors would condition us by making us tread water until our lips (all of us) turned blue. The well insulated among us had a better time of it.

    Pantone is a familiar way to go for printers’ spot colors. Munsell provides a more systematic and rigorous reference chart for generic science types who aren’t color specialists. Of the models used by designer types for describing colors numerically; RGB (for computer) and CMYK (for pigments) are common (but not used exclusively).

    One caveat, color perception is strongly influnced by context. These dogs are colored the same:

  4. Bollocks them dogs coloured the same! I looked and looked and even though I know about the context issue my eyes absolutly 100% wont let me percieve the sameness.
    I will swear in court they are different!
    Wow. Great image. Thanks to the commenter O Applesauce for it. Might show it at a weekly saftey meeting as an example of a situational awareness issue.
    I was reminded of the Mcgurk effect actually, which is a pretty neat thing too, for those unfamiliar with it.

    1. Hat tip to WaPo for the doggies:

      They have some other examples there that are easy to verify by covering part of the image with a finger. (It’s just that I’m a sucker for critters.) Some of their images are of poor quality though.

      There’s an xkcd one there that’s pretty good, which references the now famous dress.

  5. An excellent discussion. I’m sure everyone reading Greg’s title question read it as he intended: “Is [human] blood ever blue?”

    I’m equally certain that everyone posting here knows there are creatures whose blood is not red — the best known probably being the horseshoe crab.

    This article in Vox gives a good overview of the various blood colors and their chemistries.

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