I have used comfrey-infused olive oil and it makes a beautiful green shade.
However, do dry your leaves first. If you infuse oils with fresh botanicals, you are likely to get mold.
Regarding superfatting, it's also called lye discount. As explained previously, it's the excess amount of oils above and beyond what will react with the lye. There are many good reasons to superfat - to compensate for small measurement errors, for example. Additionally, the saponification values for individual oils are not 100% accurate. They are estimates and individual batches of oil vary somewhat. The SF provides a margin for error. 5% is the minimum I would use for safety. For comfort, I prefer 8-10%. I live in a dry climate and tend towards dry skin. Hope this helps!