I think it depends on where you're holding it. We had dinner catered for all of our guests at an outdoor music venue that is special to us. So, it was pretty casual. I still wore a cute, white sundress. But, everyone else was casual. It was the perfect rehearsal dinner for us.
I wore a jumpsuit already in my closet, not white. Wear whatever makes you feel fantastic. And if it stresses you out to find something new or white or fancy, don't bother with it. No one will mistake you as a guest at your own party and there are no wrong choices.