The stretch map colour scheme seems counterintuitive to me. I would expect the more red to mean more stretch, but currently more stretch is represented by more blue. Perhaps this should be inverted? Or allow the user to pick their own limit colours ?
Red color indicate compressed areas, blue color indicate extended areas. This colors reflects the behavior of a material which become warmer when compressed, and colder when extended. Also, since compressed areas imply less pixel definition in your final render, it seems to me appropriate to color them as red, since red color is usually associated with errors.