I was a Mod ages and ages ago and there was NO RULE that posters could not use red.
The rule was that MODS were just like any other poster here at the site when responding to posts or starting new threads in BLACK ink....call them names if allowed in the thread zone, disagree with their posts front wards and backwards at your desire....they are just everyday users.
BUT when a MOD responds or posts in RED INK, they are being MODS, and moderating.
It was a way for Mods to continue to have fun and give their comments and be the poster they were before they were appointed and accepted the MOD position, and still be a MOD, when posting in Red.
So, if posters saw the MOD posting in Red, it meant the MOD was in their MOD role.
Care