Calculate thickness of thin muscle

thickness_all3steps

Hi, I have previously posted a question about how to measure the thickness (Calculate thickness of thin muscle) but did not come to any solution. I have followed this workflow: How to analyze the thickness of the model - #2 by lassoan and I got the result as in the attached image. It seems like the inner and outer boundary are colored, but where is the medial surface? I need it so that I can measure the thickness (distance between inner and outer boundary) of this segment. After following the workflow, what does the colors indicate?

Thanks in advance!