I've faced issues of rank (the noun) so many times it makes my head spin. Every dojo is different, but a comment from a sensei like, "I don't know where he got it..." seems rather unprofessional and aloof. In my experience, if a sensei feels that a transfer student is ready for a higher kyu, the sensei will make the student take the test and see what happens. In all other situations, my senseis have bluntly said, you're starting at scratch here if you didn't get tested in our affiliation already (most dojos seem to be like this).
Testing and rank is good for the student and the dojo for a variety of reasons:
- it makes a student focus on more specific elements before moving on
- it allows other students to observe the progress of those around him or her
- it gives a sense of confidence to older students when they work with beginners, both in the sense that beginners trust them more, and that the older students trust themselves more
- it's an additional source of income for the dojo
- it gives the sensei a chance to see what points to focus on in his or her teachings
However, I think that multi-colored belts are tacky and offensive, and I feel that pride deriving from rank is just as equally offensive, but kenshusei deserve their place in the inner circle, because if someone's willing to devote himself or herself to Aikido like that, it is their right to certain additional privileges and classes, for the safety of beginners, and for the continuation of more advanced training. I do not appreciate being treated as an inferior just because someone has a prettier belt than mine, and frankly, people who do so have some major issues to deal with on their own.
On a lighter note, if your sensei is so cavalier about allowing people with pretty belts to wear them in class, get a pretty belt for yourself. They sell them in plenty of supply stores and if not, I'm sure you can find one on-line. You could always try tie-dye!