I've accomplished this in my own sub via CSS, but it would be nice for it to be global.
For mods/admins, it's ONLY when they distinguish themselves as such that they change to green/red. If they're just posting/commenting like any other user and not distinguishing, there's no change to their color.
If an OP is commenting in their own thread, they're blue. If mods/admins are an OP AND also distinguish themselves in comments, the green/red overrides the blue.
For AutoMod, it's whenever it posts/comments - since the bot is not automatically made a moderator of subs, I colored the username instead.
Here is my CSS: https://pastebin.com/etrKGQKg