Some unusual colorful twilight may appear after volcanic eruptions. Lots of volcanic dust is spread in the stratosphere and circles around the globe. On June 12 2009,  the Sarychev Peak volcano, located in the Kuril Island (Russia), erupted. A couple of weeks later some unusual sunset could be observed in Belgium, lasting for weeks. Here an example. But, due to large scale wildfires, volcanic alike twilight colors may also appear as strong updrafts can pull the fires fine smoky aerosols into the lower stratosphere. Wildfire season usually tops late summer, so when the twilight hours arrive, don't be surprised to see this "sky in fire" far away from the destructing flames.   

This picture was taken 15 minutes after sunset. On top of the picture the atmosphere is not illuminated by sunrays, but this is still the case closer to the horizon. The Cirrus in the upper troposphere is also lacking direct sunlight, but above (in the lower stratosphere) the dusty particles due to wildfires still are. The Cirrus produces even some very pronounced crepuscular rays.           

More pictures of special clouds via this link