The kenpo tradition in the Mitose and Chow schools was to have students wear white, and instructors wear black. Kajukenbo followed that tradition in it's early years.
Then around 1958 Sijo had everyone in Kajukenbo wear black gi's. Sijo just told me that he thought the black gi's "looked bad", and that wearing black made the Kajukenbo group instantly recognized at tournaments and martial arts events. It became our trademark at the time.
Later in the late 60's when Kajukenbo started to adapt more Chinese techniques into the development of the Chuan Fa and Wun Hop Kuen Do branches, we started replacing our Japanese terminology with Chinese terminology also. That's when the black gi's were said to be related to our Chinese roots. That sounds more philosophical then admitting that black gi's just look "bad ***".
Thanks Prof.