Thank you for your answer David,
While not the exact effect I'm after, I was just wondering if you know any of the details on the transition sequence in the Wizard of Oz, when they went from B/W to color. I know the transition shot was not a pure B/W but rather a sepia. There was also a door to help isolate the transition boundaries . Was that a lighting effect or did Technicolor do some sort of optical isolation to aid the effect in post.