I think the difference matte idea is closer to what I was thinking of. It seemed like I might try to isolate the interviewee and his chair, which were foreground, using color corrector 3-way but during a quick trial, it seemed that the color of the chair (maroon leather), his shirt (lt. blue oxford cloth), and his skin tone were too far apart to isolate in one filter. (Other elements of the shot are background).
I haven’t used difference matte, I’ll have to find a description.