Attilio Anthony John Wagstaffe
Same here Sensei as you may probably know from my history page....
If I/we or my old students visited another dojo or organisation, we would always wear white belts, unless instructed by the sensei of that dojo otherwise.... It has the power to stop accidents happening to, as it served as indicator of someone's level and what they were capable of receiving, but as you know that is not always the case......
This is an interesting tactic. I can definitely see the advantages, especially if a group of people do it. I have a friend who got his black belt and asked is sensei if he could wear his old white belt when attending a seminar because he was not confident with his ukemi. His sensei refused. He said that it was disrespectful to the sensei not to show the rank that he had earned. This situation would be avoided if his dojo did the same as yours does.
When I got my black belt, my sensei had a bit of a talk with me about how wearing a black belt when training with people from other dojos is like having a target painted on you. He said he wanted to be absolutely sure that I could handle whatever sort of ukemi was necessary before he put me in that position. I guess this is another way to address the same problem.