When I go to the Daito ryu seminars, I wear a white belt now. I think when I trained with you that time, I wore my brown (I think I was 2nd or 1st kyu then, don't remember). Since I don't have rank in that art / with that group, I don't wear my black belt / hak.
When I introduce myself by mail or email to an aikido group, I let the instructor know that I am a yudansha, and ask that I can wear a white belt, as I don't know their system / training method. Now, if they say "please wear your obi and hakama", then of course I do. Either way, introducing myself ahead of time, gives them plenty of time to consider my background, think about it, and decide ahead of time.
Ron (I'm really not all *that* sneaky...the light shining off the top of my bald head gives me away...