Yep - everything turns but calendula - as far I know, too. That can be a nice look, though. I use ground peppermint leaves in my peppermint soap. They turn brown, but it looks nice anyway - just don't use a lot. If they are nice and spread out through the batter, it's very "natural" looking.
You should always use dried herbs; though I do admit to using wet calendula petals in HP once. Nothing bad happened, but I wouldn't recommend it.