In Steven Brust's Dragaera, the presence of the Imperial Orb, and the ambient energies of sorcery, have turned the skies over the Empire orange.
The overcast sky is due to the waste products of sorcery. Sorcery itself is fueled by funneling raw chaos from the Greater Sea of Chaos through the Imperial Orb.
Removed Dragaera example:
The overcast sky is due to the waste products of sorcery. Sorcery itself is fueled by funneling raw chaos from the Greater Sea of Chaos through the Imperial Orb.