I never knew until someone pointed it out to me that on Trebek J!, there was an "contestant in control" light on the lower left front side of the contestant podiums that Alex could reference when it was time to determine who had control of the board.
Also in the early days of Syndicated Joker's Wild (before the desks had the red bar of lights) there was a small white light on the side of each desk to indicate whose spin it was. Either it was so subtle or it was a rare time when they were on during a shot of both contestants.