I'm envisioning a planet around a sunlike star, with gravity and temperature similar to Mars, but covered with a thin shell of water ice (with CO2 ice at the poles). The atmosphere's pressure and composition are similar to Mars, albeit with more water vapor as would be expected due to water's prevalence on the planet.
Given the low pressure/gravity and abundance of water ice, I'd expect the atmosphere to saturate with ice crystals, similar to how the martian atmosphere is full of dust. On Mars, Mie scattering due to this dust turns the sky yellow-brown. What I want to know is, what do these ice crystals do to my planet's sky? What color is it, and how foggy does it look (if it has moons/rings, could you see them)?
My understanding is that in the low-pressure limit, ice crystals form hollow hexagonal columns of order 10 microns in length. Since they're highly non-spherical, Mie theory isn't easily applicable (not to mention that ice has very different optical properties from dust). I'm tempted to say that the ice simply turns the sky white, like the color of ice crystals in clouds on Earth, but I have no basis to assume this is still true at much lower densities and in vastly different atmospheric conditions.
For bonus points: What does the planet's sky look like near the sun? I would guess there's a halo effect, but how visible is it, given the low atmospheric density? Again, I'm not positive that this effect isn't unique to Earth-like atmospheres.