I’ve had someone attempt to explain this to me before, just why those vile green clouds. Had something to do with a combination of factors leading to the clouds “reflecting” vegetation on the ground. If that’s true, west Texas tornadoes wouldn’t have that association or at least not so pronounced. I’ve seen it several times before, it’s a very real thing. The whys and hows are a little more vague.
Actually, I'm pretty sure it has to do with mixing of predominantly blue light penetrating the thundercloud and red light from the periphery as the sun is getting lower on the horizon. This creates a green shade. However, if you ever see the green color during a midday thunderstorm, this is NOT the correct explanation.
I don’t know either but ever time I’ve seen the sky turn green it was right before a really bad storm.. and my mama yelling “get in this house!”
I witnessed those vile green clouds years ago in the SoCal desert out in yucca valley. Not too long after those clouds the worst lightning of my life occurred.