My usual attire for weddings is pretty consistent and you can see it pictured here my weddings page: http://kantabosniak.com/
Call it a sturdy bridge from that traditionalism to the spiritual/not religious” ceremony the couple wishes. It helps family members to easily and comfortably enter in to the event. I like to honor them by giving them visual and verbal cues that they are welcome, respected, and invited.
Please know that if your family is entirely non-traditional and you’d prefer me to wear a more relaxed and creative yet simple and elegant “Wise Woman”costume,” I can certainly go there, and do everyday. That’s what I call “my normal clothes.”
Other costumes for theme weddings: I’m open to exploring the possibilities!