We know that Vulcan blood is copper based instead of iron as in Humans, making it appear green instead of red. This is shown when bruised or bleeding as well as in Bones' insults to Spock.

The lips of (especially Caucasian) Humans are red(dish) because the blood shines through the skin. Consequently, Vulcan lips should be green:

Spock with green lips

Is there a decent explanation why this is not the case, both In-Universe as well as Out-Of-Universe? This would be a terribly cheap thing to do, while making Nimoy look even more alien than the ears and eyebrows alone. The fact that Spock's blood is green was established very early in the series if I remember correctly, so it is safe to assume they planned it all along.

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    Not a cannon answer but they often used green light when filming scenes with Spock. My guess is that body makeup would have been too expensive for a main character. Also, any green lipstick would wear off during scenes and show skin color beneath it. That added to the fact that no one really cared about high levels of accuracy.
    – ShadoCat
    Sep 19, 2018 at 17:19
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    Why are you showing an image of a half-vulcan to push your point? Other than that, how do you know that Vulcan anatomy for lips is similar to that of humans?
    – user931
    Oct 14, 2020 at 3:26

3 Answers 3


As the link you provide indicates, caucasian-equivalent Vulcans have not only green blood, they have green skin. (In a caucasian, most of the skin colouration is from the blood, this is why sick caucasian people tend to become so pale as their blood withdraws from their skin.)

Thus I would expect that while they may have wanted to colour the lips and skin green, it was not feasible in the budgets of the time to do more than just colour the lips. The combination of pink with green is aesthetically unpleasing to many people, so they probably decided to avoid combining pink skin with green lips, and accept it as a limitation.

Over time, people have gotten used to the skin tone of Vulcans as portrayed in the series, and as such it would be economically infeasible to use modern technology to provide the correct skin tone and lip colour.

  • 2
    People in the US at that time tended to have weired ideas concerning skin color, so maybe it was just a mistake.
    – Raphael
    May 15, 2012 at 17:58
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    The didn't flinch at changing the appearance of the Klingons with the launch of TNG/the '80s movies, though. Jul 20, 2014 at 15:13
  • @JerrySchirmer: Right but the 80s movies did not have a Klingon main cast member. Jan 12, 2015 at 22:53
  • Interesting- does this mean that Spock is a non-caucasian-equivalent Vulcan? Sep 19, 2018 at 18:10
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    Spock is half human
    – user126198
    Apr 16, 2020 at 13:43

The copper Vulcan blood only becomes green when it is saturated with oxygen. When it's in the Vulcan cardiovascular system, it has, apparently, a rust or copper metal colour.

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    That's actually a pretty plausible theory I hadn't thought about. Can you corroborate this other than with the tone of his skin/lips?
    – bitmask
    Jul 20, 2014 at 22:14
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    @bitmask This seems to be from en.memory-alpha.org/wiki/Vulcan#Physiology tho it also says oxygenated blood in the arteries is also green, it's only reddish in the veins (which, if Vulcan anatomy follows human in this area, are on the surface as compared to arteries)
    – Shisa
    Jul 29, 2014 at 12:53
  • Damn! This is really good. Sep 20, 2018 at 5:46
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    Easy to test; Find out what color the blood of a Horseshoe Crab (Limulus polyphemus) is when it's inside it's body. Their blood like some other Arachnids, a few Mollucscs and arthropods is copper-based. Oct 17, 2020 at 10:14

There isn't a canonical answer as far as I know. Everything after this sentence is wild speculation on my part.

Vulcans are said by Spock to have copper based hemoglobin, which is a somewhat erroneous claim. Hemoglobin isn't a class of molecule, its a very specific one, which is iron based. Hemoglobin belongs to a class of molecules called respiratory pigments.

There is only one oxygen-carrying blood respiratory pigment I know of that could allow for green blood but red-toned skin, and that's chlorocruorin.

Chlorocruorin is naturally green when under low pressure and red when under high pressure.

This could explain a lot of things. If Vulcans have chlorocruorin in their blood, it would mean that when inside their veins, their blood appears red because of higher blood pressure, allowing the skin to have red tones in it instead of green. Once their blood is outside their bodies, the pressure drops because there is no heartbeat to keep blood pressure up, so the blood appears green.

The problem with this is chlorocruorin is iron-based, like human blood. But, iron is just the oxygen-carrying atom. Each species that uses chlorocruorin in their blood uses a different arrangement and amount of chlorocruorin, linked together by different proteins unique to each species. Vulcans could easily have copper metalloproteins linking together the chlorocruorin in their blood.

Chlorocruorin is also known as "giant hemoglobin", making Spock's claim of having copper-based hemoglobin technically correct, if the above theory is true.

  • A very plausible explanation. Thanks and welcome to the site :)
    – bitmask
    Dec 15, 2020 at 18:27

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