Last weekend I had a player run from third to home, back part of shoe touches black rubber on plate. It was very clear that the player did not touch the 17" portion of the plate. Upon appeal the runner was called out. Is this technically correct?

No.

Speaking ASA.

By interpretation, the black is part of the plate for all purposes of play - strike zone & touching the plate (runner and defender).

I always explain it this way .....If you were to remove the plate from the ground would the black edge be left behind? Okay then, it is part of the plate.