One can get quite interesting colors int he sky, if the conditions are right, and you get low clouds over populated areas. Especially over huge cities. All the yellow lights just shines onto the clouds, making a striking contrast to the normal, blue color. Same here in this view of Paris, as seen from Tour Monrparnasse.

This is a HDR from 3 exposures, created in Oloneo Photoengine, finished in Photoshop.

Low clouds over Paris

Technique: Oloneo Photoengine, Number of exposures: 3, Camera Model: Sony a7R + Metabones MkIII Adapter, Lens: Canon 16-35mm F2.8, Focal length: 16mm, Aperture: 8, Middle exposure time: 10.0s, ISO: 100, Tripod used: yes, Location: 48.842261, 2.321754