Getting Dressed for Court
Trying a case involves standing up in front of 12 total strangers and attempting to persuade them to do something.
Whether you want them to or not, those strangers are making judgments, not just about the case, but about you - most fundamentally, whether you are someone they should listen to and respect.
And while it may be irrational and unfair, those judgments may be based, at least in some small part, on what you choose to wear in court. Because of that, your wardrobe should be respectful and moderately conservative in all respects.