Skin darkening where CAR-1 has been gripping

Hello! First time posting here but long time lurker. I've been restoring for just over 3 years now (with progress that has been a lot slower than I would've liked) and I've had my CAR-1 for about a year. Is it normal to have the skin be a bit darker in the areas where the gripper has been... well, gripping? I don't think I've been using too much tension and I don't really have any pain or discomfort while wearing it, so I was curious about it.