Most thunderstorms occur in the late afternoon. By this time of day, the sun is beginning to set. The orange hue is caused by the same process that causes the vivid colors at sunsets. Shorter wavelengths of light (blue) are scattered quickly, leaving only the yellow-orange-red end of the spectrum.The moisture particles are so small that they can bend the light and alter its appearance to the observer. These water droplets absorb red light, making the scattered light appear blue. If this blue scattered light is set against an environment heavy in red light—during sunset for instance—and a dark gray thunderstorm cloud, the net effect can make the sky appear yellow or even faintly green.
It's a pretty reliable sign of a thunderstorm,
Now, Yellow Orange and Red are the last 3 colours of VIBGYOR. Sometimes, rarely in Mumbai, we see a greenish tint also. The next colour in the spectrum. ( I have seen it once in Mumbai many years ago).
Scott Bachmeier, a research meteorologist at the Cooperative Institute for Meteorological Satellite Studies at UW–Madison: " Particles in the air scatter light. In the day, the particles scatter more violet and blue light, but our eyes are more sensitive to blue light — that’s why the sky appears blue.
Thunderstorms, (which can be the home of tornadoes), usually happen later in the day, when the sun is approaching the horizon. That creates a reddish tinge in the sky, as any fan of sunsets knows. But light under a 12-mile high thundercloud is primarily blue, due to scattering by water droplets within the cloud. When blue objects are illuminated with red light, Bachmeier says, they appear Yellow/green.
A green cloud “will only occur if the cloud is very deep, which generally only occurs in thunderstorm clouds.”
Also Understand: Thunderstorms are a great way for the atmosphere to release energy. When warm moist air meets colder drier air, the warm air rises, the water vapor condenses in the air, and forms a cloud. As the water vapor condenses it releases heat, which is a form of energy. A large amount of the thunderstorm's energy comes from the condensation process that forms the thunderstorm clouds. As the thunderstorm progresses, eventually the rain cools the entire process down and the energy is gone.