That sounds right. When I first shot Ektar I had the issue with the shadows shifting purple or blue and excessive grain showing in those shadows, I thought it looked underexposed. When I read the spec sheet exposure recommendations I just started shooting it at ISO 64 or sometimes 50 and that seemed to cure my Ektar issues. It's interesting because the Portra 400 exposure recommendations for unmetered is two stops higher than Ektar or Portra 160 which is on the overexposure side by a stop vs metered. That supports your theory perfectly and it makes sense.
Originally Posted by MattKing