Harry, I was taking pictures of my first Natural Mystic, getting ready to post, when you posted this. Mine was splitting at the top so picked it a little early. Like yours, I think more time on the vine would have helped. I enjoyed it, however, of the five types I have eaten so far it is tied with Purple haze for second place. Tops still goes to Hailey's Comet. Fourth Viet Red, fifth yellow (Selenicereus megalanthus).
It was still greenish pink on the outside when I picked it but I let it sit on the counter for a few days.
Natural Mystic on the Left, Hailey's Comet on the right: