The convention evolved early, when secure communications were rare. The US/NATO clearly marked the secure lines with bright red phones, since the major danger is sending something in plaintext rather than secure, while the reverse error is more harmless.
The green phones followed (since green is the complementary color of red), more out of cargo cult thinking than any usability purpose, which is why you'll still see a lot of black equipment (because the colour of the unsecured line is relatively unimportant.)
And now, we have a hand-me-down convention that contravenes one of our hard-wired conventions about colors:
Green: Go, Proceed, Correct, Benign
Red: Stop, Not permitted, Incorrect, Harmful.
It is odd, but much like the wrong sign on the electron, you get used to it.
Historical German KWF secure analog telephone, with example red "secure" and green "clear" buttons
I'm confused; the article you linked to consistently says it's the other way around:
- The green and red buttons at the front are for switching to SECURE and CLEAR mode respectively
- When the user presses the green button... The exchange then switches to encrypted mode
- ... Press the green button on the phone to cause the exchange to switch to encrypted mode
- In normal use... the call is not encrypted and the red LED, marked Klar (clear), lights up
- In secure mode, the red ET button can be used to switch back to clear mode again
There are a number of comments here stating that the convention is red secure/green insecure, so I presume the article's author is incorrect.
Or is this a classic illustration of UI confusion?
Huh, good catch. Either the author mixed up the description, or the designer confused the standard. I just grabbed the first example at hand, but a quick googling should turn up some more devices.
The convention evolved early, when secure communications were rare. The US/NATO clearly marked the secure lines with bright red phones, since the major danger is sending something in plaintext rather than secure, while the reverse error is more harmless.
The green phones followed (since green is the complementary color of red), more out of cargo cult thinking than any usability purpose, which is why you'll still see a lot of black equipment (because the colour of the unsecured line is relatively unimportant.)
And now, we have a hand-me-down convention that contravenes one of our hard-wired conventions about colors: Green: Go, Proceed, Correct, Benign Red: Stop, Not permitted, Incorrect, Harmful.
It is odd, but much like the wrong sign on the electron, you get used to it.