history of - Why is green considered a toxic color in movies?

In movies I often see green used to color dangerous and/or poisonous substances colored green, like green clouds of gas considered poisonous, and green acid considered dangerous. Can anyone explain this, or explain where this came from?

Answer

Because it was forever linked to poison by Radium and Green pigments in the 1800's. Paris Green and Scheeles Green in particular helped cement this association early on.

Radium Poisoning

It was clear from the beginning large doses of Radium was dangerous, the Curies made it clear early on, but it was commonly held that in small doses Radium was beneficial.

Those who painted radium watches suffered from drastic Radium poisoning, and would glow green. The radium girls destroyed the reputation of Radium, giving us the classic radioactive green glow association

What Made Green Pigments So Toxic?

Both were arsenic compounds that produced popular shades of green, known for their brilliance. They were excessively used

Paris green (copper(II) acetate triarsenite or copper(II) acetoarsenite) is an inorganic compound. It is a highly toxic emerald-green crystalline powder3 that has been used as a rodenticide and insecticide,[4] and also as a pigment, despite its toxicity.

https://en.wikipedia.org/wiki/Paris_green

So much so that Paris Green was later used as an insecticide. It was used to kill mosquitos, and in the Paris sewers to kill rats.

https://en.wikipedia.org/wiki/Paris_green#Insecticide

How Did They Respond in the 19th Century?

Green gained an ominous reputation, with tales of women in green dresses collapsing, newspaper printers being overcome by fumes, and children wasting away in bright green rooms

https://en.wikipedia.org/wiki/Scheele%27s_Green#Toxicity

Famous Deaths

It's widely implied that these green pigments contributed to Napoleons death due to the lavish green suite he slept in.

There are also reports it caused health issues with famous artists who used the pigment, such as blinding Monet

Other Dangerous Colours

There are other colours with similar associations, I would recommend this Ted Ed video