Really awesome and well executed. I'll be using this for sure. One thing I don't get is that you click a muscle group and sometimes it turns red and sometimes

Really awesome and well executed. I'll be using this for sure. One thing I don't get is that you click a muscle group and sometimes it turns red and sometimes pink. What is the difference? And then I click on the opposite muscle on the back of the body and the front disappears. A bit of twiddling to get it right. Maybe a small animated intro with how to would help here.