Now, I'm no expert of course, but I've read up a bit about herbal/botanical additives, and everything I've read says that they are naturally going to discolor the soap, and there's not much you can do about it. I don't know for sure if dried herbs would work better or not, but it seems logical that they would, depending on the herb/additive. I'll leave that for someone else with more experience to answer definitively.
Instead of putting them in the soap, you can put them on the soap. But whenever adding any extras, remember, less is more. It is very easy to over do it and make the soap too scrubbie and rough on the skin.