It is not my intention to assume what obi anyone should wear, rather just note many things have changed in the past 100 years.
There was a time no one on Okinawa wore any specific obi during their karate practice. It is generally assumed when karate migrated to Japan in the 1920’s it’s use was adopted (along with specific training uniforms) appropriated in principle from obi use in Judo. Different colors showing where a student/practitioner was in their practice.
But many practices developed in Japan finally were adopted on Okinawa too. It is generally assumed dan rank was first established on Okinawa during the 1950s. Then dan any kyu rank became the standard, that and group specific obi traditions.
And from the use in Judo, the senior instructor began to wear a red obi (or in some cases a white obi.) But more time passed, and the entire world began to adopt their own karate obi traditions.
Some on Okinawa even went to Obi such as Gold Obi. The groups developed their own standards on that.
This is just an example that even on Okinawa, the martial art of karate is constantly changing.
"Since Karate is ever-advancing it is no longer possible to speak of the Karate to day and the Karate of a decade ago in the same breath...Karate in Tokyo today is almost completely different in form from what was earlier practiced in Okinawa...
Precisely because it has its own life, do is subject to the inevitable cycle of growth and decline. It is ever-changing, but only in its outer form. The basic nature of do remains immutable."