Blue is a rare color in nature. If you think of one random organism, there's a high chance that the organism won't be blue. That's why some filmmakers use "blue-screens."

But what if there exists a world where all creatures are blue--where the flowers, trees, and birds are all shades of blue?

So, is it possible that all creatures (limited only to animals and plants) are blue? If so, how?


  1. All-blue, as in only all plants and animals are shades of blue. The environment (like the ground) doesn't have to be blue. There could be some gray here and there, but mostly shades of blue.
  2. No colorblindness solutions. This is because red-green colorblind vision would mostly see in black and white with occasional blue.
  3. I would prefer a scientific solution. So a world where all animals are blue or evolved to be blue because of a certain environmental factor (what is that environmental factor?).
  4. By world, I'm just meaning one life-sustainable planet.
  5. I'm asking if this is realistic, so no fantasy or magic.
  6. The world doesn't have to have Earth-like conditions. There could be different types of organisms than Earth and different environmental factors. There doesn't have to be intelligent species like humans.
  7. On Earth, basically everywhere you go, you see creatures (insects, plants, humans). The blue world should also be densely populated with creatures (it doesn't have to be as much as Earth, though).
  8. Biodiversity. There are an estimated 8.7 million species on Earth, and this blue world also should have a similar level of biodiversity.
  9. If blue isn't possible, another color would be okay.
  10. If blue plants aren't possible, only blue animals would be okay.

image from Google

Basically, a world filled with only these types of creatures

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – L.Dutch
    Oct 19 '21 at 3:33
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    $\begingroup$ Yo listen up, here’s the story of a man that lives in a blue world $\endgroup$
    – Nephanth
    Oct 19 '21 at 6:17

10 Answers 10


I think you are starting from a false premise

Blue is a rare color in nature.

It would be more correct to say that our eyes are made in such a way that we don't see that much blue around, because they are not so sensitive in the UV part of the solar spectrum.

Just give a look at how different birds see the world around us (of course the rendition of the bird vision is done in human terms, so it's not "true").

enter image description here

Simply said, what we call color is just a sensation created by our brain when processing the signals coming from our eyes. We cannot even be sure that what we call "red" is the same for everybody (and many languages do not agree on the colors, either).

Anyway, if you want to have a blue shaded world, just shift the star emission more toward the blue side of the spectrum, this will steer the evolution of sight to be blue centered instead of yellow centered like with our Sun.

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    $\begingroup$ Be awarw that a bluer star would have much harder hotter radiation too. Check this isnt a problem. $\endgroup$
    – Stilez
    Oct 18 '21 at 8:39
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    $\begingroup$ "this will steer the evolution of sight to be blue centered " - I'd presume that, in order to fulfill the conditions of the question, a human observer should see those creatures as blue. Otherwise the local creatures could see whatever they see and call it "blue". $\endgroup$
    – vsz
    Oct 18 '21 at 12:03
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    $\begingroup$ But humans would see no more blue even with UV-sensitive eyes - we'd simply see UV, and I see no reason why that would necessarily be described as "blue". Blue light is about 450nm in wavelength, UV is <400nm. It's not like there are other wavelengths of blue that are invisible to the human eye - if the human eye cannot perceive it, it's not blue, which is by definition a visible wavelength. I don't see why a UV-reflective bird would be considered "blue" if it's not reflecting light in the 450-485nm range. $\endgroup$ Oct 18 '21 at 13:36
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    $\begingroup$ The sun is not yellow. It's about as close to white as you can get, containing almost the full visible spectrum with only a few small gaps. The only reason we perceive it as yellow is by contrast against the blue sky. It is in fact, more blue than most sources of light - most artificial lighting, including fire, tends to be very yellow compared to the sun. $\endgroup$ Oct 18 '21 at 18:20
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    $\begingroup$ @jamesqf I don't know if that's accurate, the idea that the Sun is yellow seems to be one of those universal ideas throughout the world and history. Even NASA is in on the conspiracy! $\endgroup$ Oct 19 '21 at 8:09

From my small knowledge of biology, animal colour is either to hide the creature or to highlight it. So if there is a significant variety of predators then almost everything would want to camouflage, prey to stay hidden, predators to sneak up on the prey. so if on you planet, instead of the browns of bark and the greens of leaves, you have instead both the bark and leaves to be blue. Then the best colour for camouflage would be blue.

Plants on earth mainly use 2 chemicals to adsorb light to "eat", Chlorophyll A & B, they mostly adsorb light in the red and blue sections of light, leaving green, so when light hits the leaves the plant adsorbs the red and blue light and the green light isn't adsorbed. That is why leaves are green. So if your planet's plants use a different chemicals that adsorb the green and red light then they would have blue leaves.

As to why the plants would use the green and red light, if the star that your planet is orbiting is slightly colder (about 1000°C colder than the sun) then the peak in the intensity verse colour, will be on the green yellow boundary. Compared to our sun where it is on the blue-green boundary.

Bark gets its colour from a collection of chemicals called Tannins, where they are used to discourage things eating the plant, again if the plants on the planet have compounds the do the same job but are blue then you would have blue bark.

A point to mention is that most blue animals get their colour from structural colouration, where the colour comes from microscale structures causing, compared to having a pigment.

hopefully that helps

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    $\begingroup$ you don't even need to justify why the plants are a different color, earth plants are green due to pure random chance. $\endgroup$
    – John
    Oct 18 '21 at 21:24
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    $\begingroup$ @John, not pure random chance. Given the Sun's emission spectrum, chlorophyll is one of the better choices for absorbing the available energy. $\endgroup$
    – Mark
    Oct 18 '21 at 22:09
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    $\begingroup$ @Mark Chlorophyle is horrible for absorbing the available spectrum, look at something like Bacteriorhodopsin which absorbs a much wider and more abundant portion of the spectrum. Nearly the entire visual spectrum, that's why plants need to produce so much chlorophyll it is a poor absorber. $\endgroup$
    – John
    Oct 18 '21 at 22:47
  • $\begingroup$ @John I've read somewhere a theory that stated chlorophyll is more stable because it is less absorbent and therefore better suited for plants (and not just random), so it might not be just random chance $\endgroup$ Oct 19 '21 at 18:51
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    $\begingroup$ Chlorophyll was a selective adaptation to compete in an environment where absorption of different light wavelengths was dominant — by anaerobic purple bacteria especially — during the Archaean eon. Not much oxygen, and red and blue light was left for the taking. As oxygen became more prevalent, the purple bacteria were pushed into niches, and it was also necessary to protect against oxidation, which may have further advantaged chlorophyll over other photosynthetic molecules. cell.com/fulltext/S0092-8674(00)80144-0 $\endgroup$ Oct 19 '21 at 21:22

Copper Sulfate

Your planet's creatures need lot's of copper(II) sulfate as an essential nutrient for some metabolic process. Copper(II) sulfate has a bright blue color when dissolved in water, so as long as your planet has a lot of it as life evolves, it may be incorporated into some metabolic process. Admittedly this is unlikely, due to copper's density and rarity, but if for some reason your planet's crust has lots of copper, acid rain containing sulfuric acid, and not much water, it may appear in significant concentrations in the water. If this is the case, all cells may have large amounts of Copper(II) sulfate within the cytoplasm, giving all the cells a blue color.

If this evolves early enough in the history of life on your planet, it may become integral to a number of processes. This means that if there was an evolutionary pressure to be a color other than blue (which there will be), Copper sulfate would be too important to get rid of.

Note that copper sulfate is toxic to much of earthen life when ingested, and is in fact regularly used as an herbicide. Humans probably won't die from just standing on the planet, but I would advise against drinking any of the water there, or eating any animals native to there, or swimming in the water on this planet.

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    $\begingroup$ copper based pigmentation is a cool idea, but copper sulphate might not work to well as it is quite soluble. A possibly more biologically stable compound would a copper ion in a porphyrin ring (they are the same type of compound that surround ion in the blood, that stabilise iron in blood to give it the red colour), tweaking the exact porphyrin ring would allow you to have variation in colour. This answers talks a bit about porphyrin pigments $\endgroup$
    – Nyra
    Oct 18 '21 at 7:45
  • $\begingroup$ That makes sense, I was just looking for a blue compound. Although the water solubility issue may not be a problem if the water on the planet naturally has high concentrations of copper sulfate $\endgroup$
    – user88782
    Oct 18 '21 at 18:46

Their genetic material is a dye in visible wavelengths of light

Our DNA is actually a very good dye - we just don't see the ultraviolet frequencies it absorbs in. If you look at a table like this one, plain DNA absorbs UV light about as well as protein that has been dyed by various procedures (Lowry and so on) absorbs visible light.

Your planet's lifeforms have a genetic material that absorbs a broad range of reddish frequencies. While anyone with a sunburn (or a melanoma) can tell you that having genetic material absorb light is a BAD idea, it has been known to happen. At least red light has less energy per photon and is less likely to catalyze an unwanted chemical reaction. Additionally, it is more plentiful, a source of photosynthetic energy for plants. Perhaps life originated on your planet that was capable of photosynthesis from the very first molecule.


One thing to also remember about the "Blue is a rare color in nature" is that well, you're discounting a huge chunk of life that lives "Under the Sea". Do to the properties of water, red is not visible underwater from a shallow depth of 20 feet and as the depth increases, the higher end of the color spectrum starts to fade. By 60 feet, most things look Blue or Green because that's all that can be seen. There are a number of blue marine life, but there are also several land animals that are blue.

Among marine life, we have the Leatherback Turtle, which is a grey-ish blue color, the Blue Whale (largest animal ever known), the Beta Fish or Siamese Fighter (though the blue coloration is caused by selective breeding by humans and more prominant in males as males are more desirable for sale), some species of parrot fish, Angelfish (including the blue and yellow striped Emperor Angel Fish), sharks (including the Blue Shark, and muted blue whale shark), the Blue Crab (as a Marylander, I see these things live in the store and it's a very bright blue) and quite famously among Pixar fans, the Blue Tang (aka Dory from Finding Nemo, who is, as she claims, a natural blue).

Terrestrial Blue Animals include Blue Macaws, several species of lizard (including many with blue tongues) the Blue Poison Dart Frog, Tree Frogs, Blue Penguins, Casowarys (nasty birds), Blue Jays, Humans (blue eyes seem to be recessive, though many adults with eyes of different colors had blue eyes as babies), Grand Cayman Iguanas, as well as the ever famously named Blue Footed Boobies.

As for the use of Blue Screens for special effects (AKA Chroma Key Compositing), you forget that it's way more common in the industry to use Green Screens rather than Blue (Green being the most common color in nature, thank you all the world's plants ever). The reason blue is used has nothing to do with natural colors. Chroma Keying was developed in the 1930s and blue screens were used prior to CGI because the film could be chemically treated to turn the blue back drop clear on the film, and then over lay the remaining images onto the backdrop that will be used in the final product. Green Screens were much more favored in television production because local news used Chroma Keying for weather reports and meteorologists tended to wear navy blue suits on TV. Green Screens were also used in films where characters were expected to wear blue colors (Superman was green screen because he wears alot of blue.).

With the advent of computers and CGI, the background color for Chroma Keying can be any color you want it to be. I've done photo shops using a white backdrop because it was all I had on my budget. Blue and Green are just common because it's what everyone in the industry always used and it ain't broke.

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    $\begingroup$ any color could be turned clear on film, blue was preferred because it had the finest grain chemically and thus the best resolution. Green is better once you have digital because the bayer pattern samples green twice as much as any other color (done because human eyes also have more green cones) thus it has twice the resolution of red or blue. the weatherman thing is an urban legend. $\endgroup$
    – John
    Oct 18 '21 at 21:33
  • $\begingroup$ @John Not so much an urban legend, but more that it's something that weather reporters (and regular TV anchors these days) need to be aware of with wardrobe choices. It's certainly not an urban legend that mistakes have happened here. :) $\endgroup$
    – Graham
    Oct 19 '21 at 10:06
  • $\begingroup$ @Graham the idea that that is WHY we switched from blue to green is an urban legend, not that spill is a thing. $\endgroup$
    – John
    Oct 19 '21 at 20:48

Solar Output + Evolution

Looking at the way life on our own planet has evolved can give some possible clues as to how another planet might see life adapt under similar, but not identical, circumstances.

The spectra of our star, Sol, peaks right around the 500nm wavelengths that correspond to green light (as we'd expect for a blackbody radiation source with temperature ~5800K). As such, when organisms started evolving chlorophyll and similar compounds to take advantage of solar radiation as an energy source they evolved compounds that could efficiently absorb light in those most abundant visible wavelengths. Presumably, if that were the whole story, then chlorophyll wouldn't be green because it'd be too efficiently absorbing green to reflect any back to our eyes... but if these models are correct then sacrificing some peak-power efficiency for smoother steady-state operation can actually be a net-benefit trade-off that favors absorption at wavelengths to either side* of the peak output rather than dead-centered on the peak. (* The wavelengths are on the "shoulders" of the peak where solar output is still high, though.) Then, since chlorophyll evolved to be green, plants evolved to be green, and lots of animals evolved to camouflage themselves against a background of green plants.

So, based on that line of cause-and-effect, to get blue animals we'd need: a background of blue plants, which would require "blue chlorophyll" centered around something like a 450nm wavelength, which would require a solar output corresponding to a blackbody temperature in the ~6500K ballpark. Basically, your world just needs a 12% hotter sun.

Do note that this line of reasoning doesn't really say anything about the browns and blacks that are so ubiquitous in our world. Presumably, being a jet-black night predator is just as important there as it is here, and evolving broad-spectrum absorptive pigments as "sunscreen" to protect from solar radiation is just as important (if not more-so due to higher UV levels); so, you're still likely to see plenty of browns and blacks over there.

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    $\begingroup$ green is not adaptive in earth plants, not since before plants were eukaryotes anyway, earth plants are green due to pure fluke chance. they were just the first photosynthetic organism to pair with a eukaryotic cell. whatever color that organism happened to be is what color "plants" would be. $\endgroup$
    – John
    Oct 18 '21 at 21:28
  • $\begingroup$ @John Firstly, I do believe my Earth history intro states "when organisms started evolving chlorophyll" rather than specifying only high-order plants, and my backtrack-chain does specify "blue plants" and "blue chlorophyll" as two separate steps. Secondly, "fluke chance" doesn't grasp the probability landscape properly; presumably absorbers tuned to X-ray, Radio, or Terahertz should be significantly less likely to reproduce (and/or be preferentially evolved toward) than replicators tuned to more commonly encountered radiations of their nearby blackbody star. Green wasn't necessarily first. $\endgroup$ Oct 19 '21 at 3:10
  • $\begingroup$ green was adaptive back when halobacterium were the dominant photosynthesizer, for non-competition, but once chloroplasts bonded with eukaryotic cells, the color got locked in and they are stuck with it even though they no longer have competition. $\endgroup$
    – John
    Oct 19 '21 at 20:35
  • $\begingroup$ @John So, what is the critique? My loose use of the word "chlorophyll" when "photosynthetic pigments" is the more correct term? Or the fact that I'm not treating the chloroplast color "lock-in" as highly arbitrary and mostly cut-off from further evolutionary pressures moving forward? $\endgroup$ Oct 19 '21 at 20:56
  • $\begingroup$ the idea that you would have to change the suns output to get "blue chlorophyll" $\endgroup$
    – John
    Oct 20 '21 at 9:16

To me the question is more along the lines of 'Is it possible to have every exterior part of every single living thing of 3b+ species on a planet' not reflect more of any color than x' (x because you said blue was just your first choice)

And to this, the answer is 'no, mostly'.

Radiation is one of the few energy gradients steep enough for life to latch on to - and if it is bright and hot enough to see by (which your question implies; 'blue' does not track for a world bathed solely in NIR, with beings only vision being in NIR, for instance), it would also be a viable source of energy, which would be used, because evolution (even if other energy gradients, like chemical gradients were the dominant source). - If visible radiation is present, there is no evolutionary pressure to restrict the reflectivity to specific spectra - blue pigments might have some chemical drawback that makes them too cumbersome to have, but as the reflective spectrum can also be shaped by physical properties (e.g. gratings), and vision would be a form of communication, there is simply nothing that would preclude some creature from being not-x-colored, for at least part of its lifecyle. If everything is non-x-colored, being x-colored will be so incredibly visible, it would be irresistible to occupy that ecological niche for reproduction, dazzling, anything.

Unless there is evolutionary pressure to do that. Have botswarms circle the planet wiping out everything non-x-colored? Presto: nothing x-colored evolves. (This might only work for bot-visible parts - if some creature has non-x-ish innards, that are not visible unless the creature gets gutted, that might be a blotch of color the bots do not get to before it is too late (shooting a corpse will not affect its viability...))

If the planet has no natural light source, and everything evolves in darkness, again, there is no evolutionary pressure against non-x-colors. Because how could there be? There might be pressure towards specific colors (incidentally, as a byproduct of some chemical reason), but that does not preclude some outlier from using some chemical or physical facility that, besides the main evolutionary attractiveness, also reflects light in a way to seem blue. (Light from the torches of explorers, that is)

So 99% x-colored ? Sure. 100% ? Nah. Unless color-seeing killbots are in the picture.


Worldbuilding isn't reality… that's the point of world building.

In reality, the all-blue world won't work.

In worldbuilding everything including all creatures - and plants, and minerals - being blue depends solely on the builder's abilities.


Sure, through natural selection.

Essentially, imagine your world fits the following criteria:

  1. The flora - the grass, the trees, the leaves, the plants, or whatever your planet's equivalents are - are for the most part, blue. You can justify this with another answer's reasoning.
  2. There is at least one superpredator species. Its intelligence and ferocity is so incredibly intense that species which fail to camouflage themselves within their natural surroundings are rapidly removed from the gene pool.
  3. Thus, the species that survive natural selection are almost always some shade of blue in order to disguise themselves in their surroundings. As a result, they can easily hide themselves from the predator species and thus not go extinct.

As I understand the question, it's asking if there's a plausible scientific reason that life on a planet might by (mostly) blue to the human eye.

If all light reaching the planet is blue, then this becomes an obvious "yes", and makes the creation of blue-only images easy :)

As @hszmv mentioned, one way (and arguably the easiest) to do this is to place the planet surface underwater.

Another might be to place it under ice: massive ice caverns. People typically wear red to be visible when exploring such caves, but if you google image search "Glacier cave", you will see that the people within them mostly look like they are wearing black/white/blue unless they use artificial lighting or stand near an entrance where the light is unfiltered. And the overwhelming color of that image search page is blue.

Deep cloud cover could also do this, perhaps, but it would probably need to be very deep.

Finally, something else in the atmosphere and/or in the star itself could be blocking sunlight so that only a narrow band of wavelengths of visible light reach the surface: 450–495 nm.

This is a definitional issue. Arguably, none of this means that the creatures and plants there are blue, if exposed to white light: just that, in their natural environment, which is what I assume you'd be drawing, they would look blue to a human eye.

A photograph of them using an Earth camera without a flash would show them as blue; with a flash (so, adding artificial white light) they might be a rainbow of colors, unseen to themselves, or visible only when near bioluminescent animals.

I'd expect that most bioluminescent animals would also tend to be blue-glowing, though, since 1) if the filtering is atmospheric, it's the light that travels farthest, and 2) either way, it's the light that eyes are most sensitive to.

There might be a significant benefit to bioluminescence that's far outside the blue range, though, if it means the glow would be visible only to creatures adapted to see that color. This could allow artistic use of small points of contrasting color.


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