Something I learned today:
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 green.
Now you know.