Very very interdasting catch.
In top secret facilities, like inside a SCIF, the wiring and infrastructure is classified as "Red" or "Black". Red is that which carries classified data in the clear, i.e. in decrypted form. Black carries encrypted data. So the "red" is the meat, so to speak, that needs to be protected from eavesdropping.
Just free-associating here. Pic related from January 12, 2018.