Re: The logical next step is the two-dimensional risk rating approach
Blame that on nature.
Generally speaking, in nature, dangerous animals (poisonous) tend to be brightly coloured, with red being liberally used.
Therefore it is natural to associate red with danger.
If you reverse it, you will have problems. Try teaching kids that in nature anything red should be avoided, but in industrial/technical contexts, red is good and green is bad...
So, avoid that snake with a red belly. But that bright red button is the good one, the one that opens the door, but the green button is the emergency "vent reactor" button.