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

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?