I've seen umpires who wear bags that match the shirt color, if their uniforms are pressed and creased it does look good. I always go with the same color as my slacks, that works for me. I also have no trouble with patent leather shoes and belts, again, if the uniform looks good they add a nice touch to it. I don't use them, but again, if the guy takes pride in his uniform you can tell, and it looks fine. this is of course my opinion.
if your shirt has white in the trim, or is white, then a white T-shirt is fine. I tend to wear Black under the cream shirt, and whatever the trim color of the shirt I have on is. I do have a number of colors shirt wise, so as you can imagine there are a lot of possible combinations. I get bored with the basics, very simply. Like to add some color to the uniform.
The dork comment didn't read to me as a joke, sorry, maybe it's how I read it. If I misread your intent then you certainly have my apology