Raederle
It is lovely on the scalp isn't it?
I doubt that it has altered your colour much.
It needs more time to do that effectively and from the non slip you are getting, the catnip may not have gotten directly on to the hair shaft - any conditioner or othere residue there would prevent that from happening completely.
ETA: Any colour that you might get will wash out easily enough. It is not any where close to a permanent stain.