There is a checkbox to turn off last-move highlighting in online chess.  But no such box exists for the Tactics Trainer.  This causes board vision issues for me for some reason.  Is there a way to turn this off in the Tactics Trainer?

Try going to your Online Chess Settings page at http://www.chess.com/home/echess_settings.html and then unchecking the box for "Move Highlights" and then saving that updated setting. I believe this should also affect the Move Highlights for the Tactics Trainer as well.

I would have thought so too, but it doesn't.  The settings for the Tactics Trainer are completely separate.  As far as I can tell, there is no way to turn off last-move highlighting in the trainer.

your wish is our command :)