I started the process of making artwork for an Ammonia World and realized that despite all my previous research on their abiotic and biochemistry, there was one thing I never quite settled on; what the atmosphere should actually look like.
Air Pressure: ~2.8 Atm
Composition: 65% N2, 24% NH3, 10% CH4, 1% C2H4, NH3 partial pressure highly variant on temperature
Temperature: About -60 to -50 C
Gravity: ~1.2 Gees
Parent Star: K Type
On the one hand, there's a lot of methane, which tends Uranus and Neptune blue. On the other hand, aside from the ammonia, this is similar to the chemical makeup of Titan, which has that deep tholin haze that makes everything orange. This also differs from Titan in that the air pressure is higher, the sunlight is stronger, and the gravity is higher, so the actual air column height should be much more compact.
I figure there should still be some photochemistry going on in the upper atmosphere, but I'm not sure if this would make the planet as hazy as Titan. There are other questions on the stack that discuss methane-rich ammonia worlds, but I haven't seen the issue of photochemical haze come up. My intuition is that the denser air and more compact column might produce a thinner haze layer in the upper atmosphere, not thick enough to turn the atmosphere opaque, but I have no idea if this is right or if it would affect the sky color. This could be good though if right, as I've seen papers suggesting tholin hazes on Early Earth may have screened UV light, which would be a boon for a life-bearing planet with no ozone.
So, thoughts? Blue sky? Uranus-like light blue? Orange? Blue with really orange sunsets? I've spent the entire evening wracking my brain about this and can't figure this out, and it bugs me.
I got the below in Terragen by assuming a bit of haze and giving the atmosphere an orange "Haze Horizon Color". Looks interesting, just not sure if right.