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It would be useful for a story I'm working on to color the world or various dominant parts of it red. I'm trying to look into the following alternatives, but am open to further suggestions. Essentially I'd like to know what gives some things their color and how this could be plausibly explained to be red on another planet.

1) grass and vegetation: as far as I understand, plants are green in order to absorb a particular wavelength of light, but it is unclear to me why that one color in particular. Is it feasible that a different type of sun would give rise to red plants?

2) water generally: both rivers and the ocean; to us it appears blue, but could it appear red and how/why?

3) the clouds. What makes them white and can they be red on another planet?

Finally, I'll probably settle on just one such element, but I'm curious as to whether all could be coherently part of the same world.

Following on the great answers provided I want to further clarify the following:

Would humans living there/having evolved there see things other than red, and humans coming from Earth perceive more of the red? Would the skin of indigenous people be/appear red to visitors? (And not vice versa). Could it be that foreign humans see things reddish, while indigenous humans see them... how? Normal?

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    $\begingroup$ Have a look to.... tada: Mars. $\endgroup$ – Ghanima Apr 28 '15 at 21:54
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    $\begingroup$ 1) Fall in New England; 2) Water usually looks green/gray/brown rather than blue; 3) Sunrise/sunset. $\endgroup$ – jamesqf Apr 28 '15 at 23:05
  • $\begingroup$ Make the sun red, or the upper atmosphere red for some reason. $\endgroup$ – Resonating Apr 29 '15 at 0:44
  • $\begingroup$ Not good enough to be an actual answer but what if you made your visitor(s) colorblind? I am not very well versed on the topic of colorblindness but maybe they could only see various shades of red. This could come and go as much as you want. $\endgroup$ – unknown Apr 29 '15 at 6:42
  • $\begingroup$ @Ghanima Interestingly, Mars is apparently "not red" after all, at least below the surface: zmescience.com/science/mars-curiosity-blue-dust-03022015 $\endgroup$ – talrnu Apr 29 '15 at 13:51
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I am going to ignore many of the more philosophical point on color, and really just focus on what could make a human visitor see mostly red (light of wavelengths of about 620-750 nm).

Making the Sky Red

The sky is blue, on earth, for many different reasons. The simplest thing to blame for the earth's blue sky is Rayleigh scattering. This is kind of complicated, so most children do not get this answer when they ask why the sky is blue. The short explanation is that the sun's light, which does not produce an even amount light of all wavelengths, get scattered as it hits the atmosphere. The shorter wavelength light, blue light, get scattered more easily than the red. So, when the sun is overhead, you see the scattered blue more than the scattered red.

Rayleigh scattering is also responsible for the colors at sunset. More atmosphere means you see the other wavelengths getting scattered more than the already-gone blue. A simple way to produce this color on a planet would simply to have a thicker atmosphere, so the blue light gets scattered before it reaches the surface.

Red Water

We actually have red water on earth. It is just very rare to see it. Check out the Blood Falls of Antartica. The color of Blood Falls is due to a lot of iron in the water. If Mars had oceans, it would be likely be deep red due to the amount of iron found there.

Red clouds could, in theory, be done if the dust on that world was iron. It is also prudent to mention that, if the light a world receives is mostly red, things which would be white will appear mostly red. This is due to the fact that white things merely reflect most light at most wavelengths, so a white thing that only has one color to reflect will look like it's that color.

Red Plants

There are already red plants. There are all sorts of red-leafed plants out there; just do a google image search for "red leafed plants". To make the majority of plant life red is a tricky proposition. Chlorophyll are green because they absorb red and blue light. Scientists are unsure why green is reflected, so there is no reason to color hypothetical plants to be any color.

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    $\begingroup$ I was considering the iron heavy route to red clouds, but I had to eliminate it as the iron dust would just act as a nucleus for the water droplets to condense around...so I doubt it'd stay in the atmosphere too long and would probably be seen as white as the water coating the droplet would reflect all light. Maybe I'm missing something here that would let this cloud appear red? $\endgroup$ – Twelfth Apr 28 '15 at 22:35
  • $\begingroup$ @Twelfth clouds already do use dirt to form. Not much, but it's there. If silica and other dirt particles can be there, why not iron? $\endgroup$ – PipperChip Apr 28 '15 at 22:53
  • $\begingroup$ Pure speculation but I'd guess the iron nucleus would definitely be possible, but it would be in a low enough concentration that clouds would be more pink than red, though the atmospheric effects and sun color could help intensify that. $\endgroup$ – thanby Apr 29 '15 at 12:51
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A quick rundown of light...

The color spectrum of red through blue/violet is the wavelengths of light our eyes are sensitive to. If a red light enters our eye, it's actually a certain wavelength that enters our eye which is in turn detected and translated by our brain into the color we recognize. So for a item to appear 'red', that item must be sending red wavelengths at our eyes. Of course most items don't generate light, but instead absorb all other spectrums and reflect just the red we see. Hopefully that makes sense...a plant is not green because it absorbs green light, rather it's green because it absorbs the other spectrum's of light and only reflects the green light that we see.

The suns light is light across all spectrums (almost all anyway, a few are blocked which is actually how we determine the chemical make up of the sun) which we see as white/bright yellow. However it's not actually white, it's all spectrum's coming at us, including red and blue. Blue is a shorter wavelength, and as such it will reflect off of things that a longer wavelength of light will not.

So your questions answered in reverse order:

3) Clouds are white because they are formed of water vapour that reflects all light across the visible spectrum (in short, we are seeing all colors to get white). 2 potentials to get them red...if only red light is hitting them then only red light is reflected and we would see them as red. Alternatively, if your clouds absorbed the other colors wavelengths and reflected only red, then we would see them as red as well.

2) Water absorbs more light as it goes deeper and deeper, reflecting only a small amount of the light. Long wavelengths absorb more readily (red) and short waves reflect more readily (blue) which gives water a blue color as more blue light is being reflected back to our eyes than anything else. Sky is blue for the same reason.

1) We do sort of have red plants already and many plants will have their young leaves in a red hue (this is actually the origin of why we're the only creature with the ability to detect red while most others only see green/blue...red leaves are more nutritious and our ancestors living in the trees had an evolutionary pressure on them to see the more red nutritious leaves). So they can and do already exist and in the right environment can be the majority of trees.

Easiest way to get the effect you are going for here is to have the sun lighting the world giving off fewer shortwavelength lights (blues) and more red ones. Red sun?

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    $\begingroup$ Only creature? You mean mammal. And "only" includes some other primates. Mammals lost the ancestral color vision during the time of the dinosaurs and primates re-gained a cruder form. $\endgroup$ – JDługosz Apr 29 '15 at 6:09
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I've seen articles about what color photosynthetic life might be on other planets, and numerous were listed. Here on Earth we have red and yellow algae as well as green and blue-green, and Venture's ocean genome survey is showing many different ways for photosynthesis to work.

Find a reason why red chloroplasts became the dominant form. Maybe lack of magnesium. The forest or plankton that shows the color of the planet might be pigmented for other reasons.

A red variety of photosynthesis mechanism may be more suitable for becoming the endosymbiote used to make the original eucaryote-equivalent plant cells and that became the established standard very early.

The star might be red, with red light being the only choice: it would look black in that light, but red to our flashlights and as lab samples.


Water looks like the stuff around it, such as the sky reflection. So take care of the clouds and beach, and the water will follow.

I recall a place where water is extraordinary blue due to the mineral content. So you could have red water (looks ok in a glass, slightly pink in a barrel, and red in a large deep body) due to minerals, salts, or life. We have "red tide" algae blooms on Earth. As noted above, if plankton were red, the world would look red from space.


Titan has red-orange clouds. Tholins are produced on many worlds and worldlets in our own system. Even Pluto/Charon has red (plains?). Mars sand is full of rust, and dust storms can reach global scale.

You'll have no trouble finding plausible reasons for red stuff, some of which could be airborne.

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  • $\begingroup$ +1 for the word photosynthesis and a reason why it might prefer red over green. $\endgroup$ – Mazura Apr 29 '15 at 8:48
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First of all – what is red? The names of the colours are merely conventions, and different people may see completely different colours, bun call them the same because they were taught to. So I'll answer a question a little bit different from yours – could all these things be of the same colour?

Short answer – no. First of all, if the clouds and the plants were coloured the same, then in the cloudy days most of this wavelengths would be reflected back into the space, while other colours would reach the surface. Evolution would kick in at this point, because the plants of any other colour will have much more energy available and become dominant, while the original species will struggle to survive and eventually will become extinct.

Though the clouds and the water are bound to be of the same colour as well. The clouds are white because tiny droplets of water scatter light – and if water was red, the clouds would absorb all the other colours and be red as well. In our life the water is quite transparent, which is more like white than the other colours, but I'm not sure on how will you explain that it is not as clear as the water we are used to.

So in terms of colours, clouds = water != plants

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Firstly I would consider the reason for a red world. What significance does red have? Considering that different colors (reflections of materials, prisms) should be possible, why did the inhabitants remove non-red natural and synthetic items? Is there a philosophical reason ingrained in said inhabitants?

For example, "suppose a man wanted a particular kind of world; say, a blue world. He would have no cause to complain of the slightness or swiftness of his task; he might toil for a long time at the transformation; he could work away (in every sense) until all was blue. He could have heroic adventures; the putting of the last touches to a blue tiger. He could have fairy dreams; the dawn of a blue moon. But if he worked hard, that high-minded reformer would certainly (from his own point of view) leave the world better and bluer than he found it. If he altered a blade of grass to his favourite colour every day, he would get on slowly. But if he altered his favourite colour every day, he would not get on at all. If, after reading a fresh philosopher, he started to paint everything red or yellow, his work would be thrown away: there would be nothing to show except a few blue tigers walking about, specimens of his early bad manner. This is exactly the position of the average modern thinker. It will be said that this is avowedly a preposterous example. But it is literally the fact of recent history." - G.K Chesterton

In other words, possibility of single-colored planet may imply the constancy of the inhabitants more than (or in addition to) the natural causes of physical red.

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  • $\begingroup$ That quote is meant to convey the idea that a person's life work is only as good as his stubbornness to that work. The colors are just a metaphor. You aren't going to see a planet painted red, no matter how badly you want it to be. $\endgroup$ – Neil Apr 29 '15 at 12:03

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