Ron
I wear my kilt to work on a daily basis, I am in the financial printing business. Recently the director of my site had her twenty year party, so I wore my Graham of Mantieth kilt, no problems in fact it quickly became the talk of the party. Even more recently one of the Vice Presidents of the company came up for a meeting with us all I was wearing my Isle of Skye, again no problems at all.
As a recovering alcoholic it has been my experience that when one is in early recovery, as your clients are they don't really care about what others are wearing, your bosses assertion that your clothes "may" prevent you from establishing rapport or connecting with some clients due to their perceptions or prejudices, is in my mind an unthinking one at best. How long have you been kilted at work before this unfortunate set of circumstances? Two years or more? Have there been any complaints regarding your wardrobe from any of your clients? I think not.
Now that I see what the reasons are I think they are utter hogwash, unfortunately you have to convince your boss that your wardrobe does not factor into your effectiveness to your clients, my wardrobe effects my work in only one way as I am sure your wardrobe effects you, it gives me great pleasure to wear a kilt, and that pleasure and freedom effects my mood, thus making me a better and more effective employee.
Best of luck with this new development I hope it works out in your favor.