I think a sensible way to do things, pilots had to get used to where they were and how things were done, plus they had to get used to new types, maybe not a great idea to do them both at once.I mentioned the P-39, because I recall reading that many groups stateside (the 99th included) were assigned P-39s and P-40s as "work up" ships.
Has absolutely zero to do with the pilot's color.