There's just the slightest tint of misty blue, because we don't really have a planetary atmosphere. We only have what we can keep enclosed in our three Habitats.
Habitat A, the "Are We There Yet", and Habitat B, the "He's Touching Me!" are like giant cruise ships, with an enclosing canopy. They are linked through very large steel arms to a Thrust Ring, which is in turn connected to the Flying Castle Habitat. Tubular elevator shafts permit spherical elevator cars to travel between the Habitats.
Each Hab is on its own time zone, with eight hours between adjacent Habs. We grow our own food, and replenish our oxygen, through a variety of agricultural ventures, including rice paddies, fish ponds, greenhouses and hydroponics gardens, and even grainfields and meadows for (mini) cattle grazing.
The Flying Castle even has natural areas that have been preserved along with the Castle and its grounds, from when we first lifted it years ago to rescue it from "the end of life as we know it", the dreaded "Last Post".
Be careful what you wish for, you might just get it.
Bob could expand on his explanation of you like.
*giggle*