I believe you need to be in a professional dress code at least when weather conditions do not matter as inside. If a pretty day outside and can get away with it you should ALWAYS be of professional dress. If you notice in the group ring and with most professional handlers men in a suit and tie and women in skirts and jackets "most of the time". Outside when weather is not so good then you can dress down.
I believe presentation plays a big part in showing your dog and being in professional attire should accompany ring presentation. Comfortable flats are a must for me! Of course traveling with a handler and watching all the professional handlers I learned it's always best to look your best and make sure the color of your clothes do not outshine your dog.
Just what I've learned in my short time of showing
Donna Bird
Brooklynn's Yorkshire Terriers