This is a photograph of Mammatus clouds over North Carolina from Rich Bruner on Earth Science Picture of the Day. According to the accompanying article,
The orange color of the clouds is attributed to a low Sun. Sunlight has been attenuated by the greater path-length that occurs when the Sun lies near or below the horizon. Here, the Sun has already set (at the surface), but the lofty clouds are still exposed to the Sun's lingering rays.