I agree with your Dean on this one. I had to buy a white uniform for my graduation years ago and NEVER WORE IT AGAIN. It was a waste of money. I've never worn white as a nurse. As a staff nurse, I wore scrubs
(as do all of the staff nurses in my hospital). In my leadership role, I wear street clothes.
Many, many nurses don't wear white these days. So, those uniforms are not as representative of our profession as they used to be. Also, many men don't like to wear the white uniforms, and I can't blame them for that.
By the way, I'm pretty sure nurses started wearing white uniforms so that they could clean out the stains with bleach. Back in the old days, you couldn't get stains out of colored fabric because bleach would discolor the fabric. Nurses wore dark uniforms with white aprons. The white aprons would "catch" the dirt and stains and they could be bleached. Look at the old nursing pictures and that is what you will most often see for a uniform. Personally, I like that look for nurses. My student uniform was like that -- a plain navy blue dress with a white apron that included a bib. I liked how it made me feel like a descendent of those previous generations of nurses.
But time moves forward, not backwards ... and nursing needs to move forward with it. The Dean is not cancelling the pinning ceremony. You are still honoring that tradition. He's just updating it to better suit our current culture. I hope you can value the traditions retained and not let a few updates ruin what should be a very special day for you.