Re: The same problem every time
Remember that some people are red/green colour-blind.
Vile creatures, mutants from the very pits of hell. Red, green, it doesn't matter what shade of grey we make the buttons, this fifth column lurking hidden in plain sight will be a constant menace to the chromaware unless we adopt the very sensible "special shape" idea Doctor Syntax hints at - but doesn't dare to elucidate.
I suggest a skull and crossed-bones shaped button, with prominent comic eyeballs over-etched with big Xs, and make this the universal sign of a killswitch by ISO code.
Just to be sure people only press it when they mean to shut down the computer, we should cover it with a shroud and put 50 000 inescapable volts on it. Also, the lifting of the shroud should trigger a three-second delay followed by the opening of the trapdoors over the pit o' snakes positioned in front of the button.