Uranus is called a green planet, although it appears blue in many of the photographs including those taken by spacecraft, like Voyager 2, Hubble, and JWST. NASA's Uranus page mentions it to be bluish-green.
One of the reasons mentioned is due to the presence of methane in the atmosphere of Uranus. But if that's the case, why can't we see this green color in the photos? I am unable to exactly grasp the mechanism behind the green color.
I think your issue is linguistic not astronomical. The way a language cuts up the space of colours into discrete names is varies strongly from one language to another, and even from one dialect to another. Translating colour names is fraught with difficulty.
Uranus has a colour that is approximated by an RGB value with approximately equal amounts of green and blue (I've found the value #B2D6DB, but monitors vary, so this isn't absolute). You might describe this as "light green-blue" or "light blue-green" or "pale teal" or "pale aqua" or "duck-egg", or some form of "turquoise".
However, the usual contrast in terms of colour is with Neptune, which much closer to an azure or cerulean blue. Uranus may not be "green", but it is "greener than Neptune".
The images below show the RGB value and a colour photo of Uranus by an Earth based observer which shows a turquoise colour
This answer looks into why Uranus is "green" or at least greener compared with Neptune's blue.
Both planets have similar atmospheric compositions and would ordinarily be expected to show similar colors. But according to a study by the National Science Foundation's NOIRLab program, the greater atmospheric activity of Neptune's atmosphere tends to break up the smog of more complex hydrocarbons which, on Uranus, tends to make the externally observed color of Uranus whiter and greener than the methane would otherwise be expected to give. The technical reference is from [Irwin et al.1](https://doi.org/10.1029/2022JE007189), and is open access. The figure below, taken from this reference, shows the brighter transmission in Neptune at blue and violet wavelengths compared with Uranus, whereas Uranus becomes slightly brighter at longer wavelengths and less blue/violet selective overall.
We actually see a similar effect on Earth. In this question the whitening of the sky near the horizon is discussed in terms of increased Rayleigh scattering, which would be caused by the smoggy conditions on Uranus too. One answer demonstrates through photography that the sky hue on Earth also tends to become greener as it becomes whiter, matching well with the difference between Uranus and Neptune.
Reference (open access)
This is just a mere illusion. In reality, the peak wavelength is actually between green and blue, that is slightly cyanish/turquoise. The reason this happens is because the atmosphere of Uranus contains methane, which has an absorption wavelength between yellow to red leading to blue/green reflected wavelength. In the albedo of 30% of the sunlight reflected by Uranus, blue green light is absorbed the most.
This wavelength is however scattered in our atmosphere, via atmosphere refraction, specifically Rayleigh scattering which leads to telluric absorption which leads to a few wavelengths being scattered more like blue wavelengths, which is precisely observed in the ground-based telescope images. In space-based telescopes where there is nill telluric scattering, the actual color is perceived.
Even though the green color is more sensitive to our light cones, green light is already absorbed by our atmosphere, before reaching our eye.
This is quite similar to how the Sun's peak wavelength is green, but we perceive it as yellow, except the atmospheric refraction is different in this case.
Space telescope:
vs.
Ground-based telescope:
It's not leaned towards pure green or pure blue. The Rayleigh scattering absorbs only few nms, like around 30-40 nm.
In conclusion:
This is a mere mirage by the atmospheric scattering of the Earth, aerosols like to absorb more green than blue due to their electrons and quantum mechanics even though Uranus is lying between green and blue.
Uranus’ color is somewhere between green and blue. Since a lot of space trivia is in the purview of elementary education, and since patterns are useful for memorizing, it’s convenient to fudge color names to fit the pattern:
*If you squint, red + yellow = orange, and brown is a dark shade of orange. Again, fudging. “thick red, brown, yellow and white clouds“. “shades of white, orange, brown and red”. “shades of white, orange, brown, and red”.
Although both Uranus and Neptune exhibit a color palette ranging from deep blue to pale green, there is a prime difference in the atmospheric composition which determines the color difference.
In the outer layers of the atmosphere, Uranus has other hydrocarbons which are heavier than methane, mainly ethane and acetylene. These substances form tiny crystals that hang in the atmosphere which causes formation of fog and it lets through waves of different wavelengths with different efficiency and it is the deep blue color that is absorbed more efficiently and leaving behind a pale-green color which we perceive. Moreover, the atmosphere of Uranus is calmer than Neptune. So, this fog is not being torn into separate bands of clouds and hence it covers the entire planet more or less evenly.
On the other hand, Neptune also has such a layer of fog but it is much thinner and cannot obscure the blue color properly as there is not enough fog to absorb it.
Source: https://universemagazine.com/en/green-planet-for-the-green-holiday/
