Abstract: A surgical instrument has an end effector and a region of stress-responsive colorimetric material on the end effector. The material has a color that changes with increases in pressure applied to tissue by the end effector, and is positioned to be visible to a user or endoscopic camera when in a body cavity engaging tissue. In some applications, image processing techniques are applied to images of the end effector captured during use and can be used to generate feedback to the user if the material is observed to change to a color indicative of a force exceeding a predetermined threshold.