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A little while back, I went to see Valerian and the City of a Thousand Planets (honestly unsure of what reaction this is going to get), and there was a particular scene that showed a desert planet's multi-colored clouds:

enter image description here

So what I'm wondering now is how to achieve the same three-tone mix of colors seen in the image above. A quick search revealed that cloud iridescence produces a similar effect, but it appears to be fairly isolated, heavily dependent on perspective, and scatters ALL colors--albeit it very vividly: enter image description here

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Clouds made by condensed water vapour will always appear white, as they scatter the light in all directions, unless, as you point out, the presence of ice crystals make them behave more like a prism, diffracting light.

If you want to have colored clouds, you need either to use dust (i.e. a dust of rust will appear dark red, sand transported by the wind give a yellow appearence to sky, clouds and rain) or colored gases (i.e. the NO2 produced in nuclear explosions is responsible for the reddish hue of the mushroom).

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    $\begingroup$ Yeah basically this, the gas colour, green for chlorine, brown for bromine, in a hot atmosphere purple iodine and there are a number of others. $\endgroup$ – Ash Sep 13 '17 at 19:05
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Much like the dust answer but how about micro-organisms that "bloom" inside the clouds. It could be that different parts of the cloud is inhabited by different types of micro-organism or that the microbe behaves differently in different parts of the cloud.

It might require a bit of hand waving to get a microbe that can easily grow to fill all the clouds but it feels like it should be possible.

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    $\begingroup$ Maybe the microbes are the cloud. They fill the air as spores; when conditions are right, they multiply as rapidly as bacteria. $\endgroup$ – can-ned_food Sep 14 '17 at 2:26
  • $\begingroup$ Cibola Burn, the fourth of the Expanse series, has green clouds in it for this exact reason. There's no multi-colouration, but it's not too much of a stretch. $\endgroup$ – Joe Bloggs Sep 14 '17 at 10:09
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Blue clouds on Mars

From https://mars.nasa.gov/MPF/science/clouds.html

These blue clouds on Mars are from a photo taken by Pathfinder. They might be water ice, or they might be CO2 ice.

From Anthony Colaprete and Owen B. Toon, Carbon dioxide clouds in an early dense Martian atmosphere. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. E4, 5025, doi:10.1029/2002JE001967, 2003

Clancy and Sandor [1998] have also suggested that the blue colored clouds observed by the Imager for Mars Pathfinder (IMP) were composed of carbon dioxide. The color of the clouds, they argued, is the result of scattering from small (0.1–0.3 mm) CO2 ice particles with particle concentrations on order of 100 cm3, forming at altitudes between 60 and 80 km.

Probably either way the blue color is not intrinsic to the composition but is due to Rayleigh scatter of light, the same as in Earth's blue sky. But blue clouds are possible.


Here is a zanier proposal: glowing clouds.

We know that noble gases can glow if they are charged under the right circumstances. These are gas-discharge lamps of which neon is the most familiar. There is not neon in Earth's atmosphere but there is some argon. argon glow

Imagine now a world where the atmosphere had a lot of a noble gas. A thunderhead contains a lot of charge and sometimes these flicker with internal lightning. If a charged cloud (water, dust or otherwise) were in an atmosphere with a noble gas, maybe that charged cloud would glow like a neon or argon light, in the color characteristic of that gas.

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    $\begingroup$ In such an atmosphere (low breakdown voltage) I suspect "thunderstorms" would become "glowing cloud storms" as the atmosphere would be unable to hold off the high voltages required to get cloud to cloud / cloud to ground lightning. Cool idea though! $\endgroup$ – madscientist159 Sep 14 '17 at 7:03
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    $\begingroup$ "The Glow Cloud does not need to converse with us. It does not feel as we tiny humans feel. It has no need for thoughts or feelings of love. The Glow Cloud simply is. All hail the mighty Glow Cloud. All hail." $\endgroup$ – Lok Sep 14 '17 at 13:33
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You could use pollution. I remember when visiting my grandparents in the 1960s, there was a factory nearby which could billow smoke in different colours. (The factory still exists, but we have had environmental laws requiring factories to clear their exhaust for a long time). With enough pollution, you would be able to get different colours.

Also note that a setting sun give clouds a different colour.

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