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More specifically, what shade of blue is the earth on average? I want to create an accurate earth-coloured blob in a simulation / presentation.

A quick search didn't turn up anything. What I found was that it is blue and why it is blue. Many of the images available online appear filtered and colours vary wildly.

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    $\begingroup$ Well, I think it would depend on where you're looking (different parts of the ocean have different colours). $\endgroup$ – jinawee Oct 19 '13 at 22:18
  • $\begingroup$ Also upon your own eyes. Every eye-brain system doesn't see the same colour as everyone else. Sometimes even both your eyes show different shades for the same colours! :) $\endgroup$ – mikhailcazi Oct 20 '13 at 5:32
  • $\begingroup$ In your place I would simply get a photo of the Earth and I would calculate its mean color. $\endgroup$ – peterh May 17 '16 at 22:01
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Well Annan, as you found out, it is a consequence of scattering of incident sunshine, so it is somewhat dependent on atmosphere conditions, sun angle etc. If you look at the color triangle, you will see that it has a straight edge from the red to the mid green, so single wavelength colors in that range can be saturated. But in the blue region, the color chart is quite curved, so even a relatively narrow range of wavelengths in that region, must result in a non-saturated pastel color; so at least you know, that no single blue wavelength can simulate sky blue.

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In Physics its called Black body radiation. look at the max energy of outgoing EM from the earth as shown in this image.

http://commons.wikimedia.org/wiki/File:Atmospheric_Transmission.png

As for how Humans views colour is a strange and challenging and different topic, one only has to google optical illusions to see that our brain influences how we see a colour not the input or wavelength.

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  • $\begingroup$ If you take another look at that plot, you'll notice that the black body emission from the Earth is not in the visible range but in the infra-red. The colour we see is due to reflected light from the Sun, not black body radiation from the Earth. $\endgroup$ – Nathaniel Oct 20 '13 at 5:51
  • $\begingroup$ Nathaniel has it about right; it's actually mostly Raleigh scattering, rather than reflection. If you look up on a clear day, you see the "blue" sky, which hides the black starlit sky from you. Turns out, the sky looks the same, looking down from a high aircraft (35,000 ft) You see the same blue sky looking down in daytime which hides the black ocean from view. Ocean absorbs 98% of sunlight, and looks black, not blue. $\endgroup$ – user26165 Oct 20 '13 at 19:00

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