The Yellow City was a city built outside of Throne by the demiurges, along with six others, that orbited it. They were immense projects, the culmination of hundreds of years of engineering and planning, that housed hundreds of thousands. Throne also used to have a moon, which harbored its own kingdom. You can easily imagine what happened to Throne’s orbiting cities, it's moon, and why the sun broke, if you consider the current state of the world and what lead there.
Au Vam, a demiurge, has been described as "Pankrator of the Yellow City," "Pankrator of Vesh, ruler of the Yellow City" "Pankrator of the Yellow City of Vesh", and the Yellow City's "king."
"Hierophant of Vesh" exists as a current title.
At one point, Par Vam was the Undersecretary of the Yellow City.
At some point, one could purchase a Void Trader's manual in the Yellow City underwarrens.
“Everyone could feel war coming. The famine washed over the land first. The dogs disappeared. The sky grew dark as the sun turned away, as if it knew what was going to happen.”
– Account from the Yellow City, circa second conquest King of Swords 6-51