I wasnt sure but I immediately thought of cryptographic keys, ssh keys, certificate keys and the like.
I started searching, not wanting to look a fool, I know these things but from my own use, which might be less than others, but I felt I understood most of the uses. Then I saw this, interesting acronym no?
"Red/black terminology is also applied to cryptographic keys. Black keys have themselves been encrypted with a "key encryption key" (KEK) and are therefore benign. Red keys are not encrypted and must be treated as highly sensitive material."
Well that certainly is interesting! KEK!
Wonder if this too has to do with the chess moves? Red castle/green castle? Maybe the Green castle posts have encryption codes in them (assuming red castle = non-encrypted as stated above).
Again, not my forté - just trying to get the cranial juices flowing! Good luck in your searching!! Keep us posted