This answer begins with:
It appears to have actually been a pole, not a cord.
Handrails and handholds, colored blue for quick identification, were located throughout Skylab.
The crewed spaceflight experience can be punctuated by critical moments where one needs to be able to access and absorb a lot of disparate pieces of information quickly, and color-coding can be extremely useful.
Color coding is also useful in warnings and reminders, e.g. "don't touch this unless you mean to".
So I would like to ask:
Has color blindness been an excluding factor for astronauts in the past?
What about currently for crews bound for space stations?
What about passengers for space tourism?
There seems to be some unofficial, non-diagnostic tests (for those interested in learning about the topic) available at https://www.color-blindness.com/color-blindness-tests/